What is Fire? Combustion Reaction Tutorial | kinetic & potential energy, heat & light | Chemistry
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- เผยแพร่เมื่อ 14 ส.ค. 2016
- What is fire? This video takes you on a tour of a combustion reaction, revealing what a flame is, how light and heat are generated, and what it is that carries the heat that we feel emanating from a flame, as well as connecting that to other combustion reactions we might experience in our lives.
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-More on Fire | Wiki-
"Combustion /kəmˈbʌs.tʃən/ or burning[1] is a high-temperature exothermic redox chemical reaction between a fuel and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion in a fire produces a flame, and the heat produced can make combustion self-sustaining. Combustion is often a complicated sequence of elementary radical reactions. Solid fuels, such as wood, first undergo endothermic pyrolysis to produce gaseous fuels whose combustion then supplies the heat required to produce more of them. Combustion is often hot enough that light in the form of either glowing or a flame is produced. A simple example can be seen in the combustion of hydrogen and oxygen into water vapor, a reaction commonly used to fuel rocket engines. This reaction releases 242 kJ/mol of heat and reduces the enthalpy accordingly (at constant temperature and pressure):
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Fires start when a flammable or a combustible material, in combination with a sufficient quantity of an oxidizer such as oxygen gas or another oxygen-rich compound (though non-oxygen oxidizers exist), is exposed to a source of heat or ambient temperature above the flash point for the fuel/oxidizer mix, and is able to sustain a rate of rapid oxidation that produces a chain reaction. This is commonly called the fire tetrahedron. Fire cannot exist without all of these elements in place and in the right proportions. For example, a flammable liquid will start burning only if the fuel and oxygen are in the right proportions. Some fuel-oxygen mixes may require a catalyst, a substance that is not consumed, when added, in any chemical reaction during combustion, but which enables the reactants to combust more readily.
Once ignited, a chain reaction must take place whereby fires can sustain their own heat by the further release of heat energy in the process of combustion and may propagate, provided there is a continuous supply of an oxidizer and fuel.
If the oxidizer is oxygen from the surrounding air, the presence of a force of gravity, or of some similar force caused by acceleration, is necessary to produce convection, which removes combustion products and brings a supply of oxygen to the fire. Without gravity, a fire rapidly surrounds itself with its own combustion products and non-oxidizing gases from the air, which exclude oxygen and extinguish the fire. Because of this, the risk of fire in a spacecraft is small when it is coasting in inertial flight.[6][7] Of course, this does not apply if oxygen is supplied to the fire by some process other than thermal convection."
Wikipedia contributors. "Fire." & "Combustion." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 27 Jun. 2016. Web. 13 Jul. 2016.
I've been looking for and wondering about how fire and combustion works. This was a simple and effective explanation - great job!
Same here haha. Gotta love Thermo
I have watched ton of videos that attempt to explain what is the thing we are actually looking at when we stare at fire, but I feel this is the only one that answered that question. Plus the explanation is unique and different from others. Awesome, thank you!
Brooo i literally looked at all videos talkin about this, but i wanted like the real physics of diré
This Channel Deserves More Attention | Simple. Scientific & Illustrated Content. KEEP UP THE GOOD WORK
so many combustion vids just describe the effects, you actually explained why it occurs. great job
Wow, this is really, really good + intuitive. I've never taken a chemistry class in my life, but this was a fantastic intuitive explanation
Thanks!
The explanation I’ve been looking for. Thank you!!
Such a great video that's explaining everything a person needs to understand the combustion reaction without any previous knowledge
Simply magnificent, well done. 🙌🏻
This is exactly what I was looking for. You gave us a little bit of thermodynamics also. Thank you!
Thank you, I'm sure most of us here already understand all the processes that happen here, but now we know how it all fits together to create combustion. Again, thanks!
awesome video. I've been wondering about fire for years. This was perfect.😊
A very satisfying explanation !
Thank you 😁
Awesome job with this explanation. Thank you so much!
thank you for explaining in depth, it helps with my revision on combustion reactions
This is the answer I was looking for. Thank you!
Thanks I have been searching for this explanation for a while! Thnx
This is great!! Thanks for such an awesome vid, awesomely interesting!
So well explained. Thank you.
fantastic physical-based description of what goes on.
Thank you so much this helped a lot it made so much sense after watching your video THANK YOU!!!😁
This is right. Good job on this.
Thank you for helping me to learn deeply and logically.
Awesome explanation, man, don't stop, people love it!
Thanks!
Great video. Most others only show the chemical equation and say " The end "
thank you, really clear explanation, great work!
amazingly clear
Just amazing !!! Clearing all doubts.
Thanks very much!
This is absolutely an amazing explaination, Ive been wandering in the internet for articles because fire really puzzles me but now, at least, I grasped the concept of why it works. Thank you so much
Thank YOU!
Thanks Really Helpful!
Very nice explanation and great animation! Thank you very much!
Amazing video!!
Beautiful vid. Thanks
THIS VIDEO IS AMAˆNG THANK YOU
thank you very much. so helpful!
Really interesting, thanks for the video !
Same
this explanation is awesome!!!!!
Thanks!
Nice simple explanation thanks!
Thank you. Much better said than my textbook
Concise and to the point. Best explanation I could find anywhere! Thanks much!
Thanks!!
@@CrashChemistryAcademy👍
Finally I found the best video
Cleared 👍
excellent video
This is the video I've been looking for.. I've never come across another that explains the heat as you did.. Thanks
Thanks-- a sort of clarification on heat-- It is sometimes said that the main carrier of heat from fire is infrared radiation. While many fires do produce IR, any IR is released in all directions. The fact that the preponderance of heat is felt above the flame is one piece of evidence that heat from fire is primarily due to released gases, which form a low density aggregate and thus become buoyant and rise up rather than disperse in all directions. It is my understanding that there is very little IR produced in methane combustion in particular (this video).
@@CrashChemistryAcademy Yeah good point about the heat of the flame and wow that's really interesting with the ir/ heat breakdown.. Like what percentage of the energy is released as ir and what percentage is released as 'really fast moving' gas molecules for a given reactant(s).. I always saw the equation in books as light and heat released in exothermic reaction.. The heat part I never understood.. But this is as close as I'll get to visualizing it.. It's kind of crazy to think that the heat portion of getting burned by conduction and convection comes down to energetic molecules or atoms 'slamming' into you really fast (besides the ir portion).. Like when a copper wire gets hot and you touch it, the burn is based on how fast the atoms or possibly electrons are moving/vibrating in the wire.. That's just crazy but I guess it's true
Yes the heat is the KE of the atoms and electrons, the burn is when that KE is transferred to your skin when you touch it. An actual burn is when your skin atoms' KE increases to the point where they begin to react with atmospheric oxygen. Not a good thing.
@@CrashChemistryAcademy Man that is so cool/ interesting, thanks
Wow. Learned so much in such a short video
great!
Reading Peter Atkins book,”Atoms, Electrons and Change.” He used Faraday’s lecture on the candle flame to introduce the same principles. Your video was a tremendous help in understanding this phenomena.
I loved reading Faraday's lectures on the candle. The guy was too brilliant. I created an entire lab for my students based on his experiments. I also love reading Atkins. I'll have to take a look at that one.
Thank you man
Awesome
enlightenment❤
In simple terms, it's nothing but electrical forces in action.
A simple way to understand why the newly formed molecules, CO2 and H2O gain so much speed after the reaction is to think in terms of electric interactions. We must place ourselves in the world of electric charges to comprehend this.
Firstly, at the atomic level the electric forces are very strong, especially when trying to bring 2 molecules very close. Also, as for the case of batteries where Zinc has an intrinsic electric potential difference from Copper called electrode potential, so does any atom or molecule. It presents an intrinsic electric potential energy relative to one another.
Secondly, we must know that at an atomic level, particles touching themselves represents a very rare and special case. Here, the atoms can't collide mechanically, but can approach each other enough that the atoms in the reactants can swap places, resulting in newly created CO2 and 2(H2O) molecules.
Now, due to the small distance between CO2 and 2(H2O) right after they form, the intrinsic electric potential difference between the newly formed molecules gives rise to the repelling forces that accelerate the molecules, pushing them apart so hard that at a macromolecular level they appear to explode. This is how the chemically stored PE in the fuel gets converted to molecular KE ( macromolecularly known as HEAT ), when released, or when the fuel oxidizes.
Note: the PE is not chemical, it's electrical in the end, so when I refer to "chemically" stored energy, what I actually mean is electrically stored.
Bonus:
To bring together the CH4 and 2(O2) molecules in the first place consumes energy. This is called Activation Energy, which may be achieved either through compression, sparks or raising the temperature of the mixture to the point of self-ignition temperature of methane.
Therefore, due to the external source of ignition, the CH4 and 2(O2) combine to form CO2 and 2(H2O) that have a lower PE and which are much more electrically stable.
So I think you probably described it pretty well. The springiness you speak of is the constant repulsions between electrons within and between atoms, combined with the attractions between electrons and any nearby protons. The constant movement of atoms is simply their attempt to minimize these attractions/repulsions, which minimizes PE, and since electrons are constantly moving everything else is constantly moving (vibrational motion, KE). I think you are right about activation energy being a large part of the final KE of the products: EA increases the starting KE of the reaction, and once the reaction gets going, the resulting lowering of PE in products transfers to an increase in KE (which keeps the reaction going). How PE becomes KE is an interesting question about which I can speculate using the physics definition of energy: the ability to do work. PE is the potential to do work, so if that decreases, the decrease is offset by an increase in the actual work done. The high KE particles produced are doing work on the surrounding air by colliding with it and pushing it out of the way: the potential to do work is being turned into doing work, thus abiding by the conservation of energy. Think of holding a rock in the air (high PE) and letting go. As the rock descends to the earth, it decreases in PE (getting closer to the earth) while simultaneously doing more and more work on the air (pushing it out of the way) as its speed increases, and then finally doing work on the earth where it lands, transferring KE to both the air and to the earth, thus conserving energy from the initial state (being held) to the final state (resting on the earth) by transferring PE to KE.... That's my best shot.
I can follow what you are saying and it makes sense from a classical physics point of view. There are however a couple of issues which may extend your explanation rather than replace it: 1) Explaining atomic behavior without quantum mechanics is very much the same as explaining gravity as Newtonian while ignoring the general theory of relativity. On a certain level it works fine, but on a more subtle level it begins to miss important details. 2) unfortunately, I have over-simplified the reaction mechanism of methane and oxygen, which actually has significantly more steps and seems to not care too much about stoichiometric ratios. (A good source of information regarding this is Peter Atkins' "Reactions: the Private Life of Atoms.") The oversimplification was done for pedagogical reasons, but as you demonstrate, that has its shortcomings. The short answer really is that you need to take a course in physical chemistry to explain what you want to explain.
@@CrashChemistryAcademy Thank you. All the best !
The things in everyday life that you never even think about.... until you're in chemistry. very interesting! Thanks!
🙂
This is great. Thanks
You're welcome!
Intresting
Thank you for this. I'm trying to understand Malcolm Bendall's plasmoid generator on howtube. I'm trying to imagine how his implosion engine is supposed to work if our explosion engines work on these principles.
Great video! CH4 (fuel) doesn't combust on it's own. It needs O2 and Heat to react. The molecules move fast (high koinetic energy) because of the added Heat. This part wasn't explained that in detail, but other than that I really enjoyed your content! Thanks!
Thanks good video.
(Now a video to explain why infrared light is emitted ^^, I must watch.)
awesome explanation
Thanks!
This is very informative and from the comments helps many people but it has by-passed the key part of the process. “Potential energy” here is an analogy for chemical energy - the energy locked into the bonds and configurations. Potential energy is a physical phenomenon, gravitational typically. Chemical energy is still the mystery here and is about the unique chemical structures and goes back to quantum mechanics which is a whole different ball-game. Why electrons in a particular configuration have associated energy is a bigger problem and needs a few of its own presentations. Nonetheless, very informative. If you have not studied chemistry, this is one of the best ways to spend 5 minutes.
Thanks for your comment! You bring up an interesting point. Chemical energy is a term often used in chemistry courses, sometimes called 'chemical potential,' or 'chemical potential energy.' However these are not analogies for potential energy, these terms all refer to potential energy of the sort you have explained in your comment, in addition to, simply, the potential for two particles to react. You mention potential energy as physical, relating to gravity as one type of potential energy. Much as gravitational potential energy arises out of the distance between two bodies, chemical potential energy can arise out of the distance between two particles that contain charge, whether they are protons & electrons, or two atoms, or two molecules, etc. It has been shown that the electrons in an ion (lower potential energy) are probabilistically closer to the nucleus than the electrons in its neutral counterpart (higher potential energy). All matter in the universe arises out of a combined potential and kinetic energy. Potential energy takes on many guises, and so has various designations depending on conditions, but it is still potential energy, whether physical or chemical.
Wow this is amazing. Thank you so much for the video. My curiosity about understanding how airplanes really fly led me here. Now I understand how Thrust is generated and thanks to you I even have a better understanding on how cars work. Be blessed!
That's great! Thanks!
So much information thanks
Good
Thank you. I've been looking for a real deep explanation of what is fire.
So if I understood right methane is a combustible on earth because the atmosphere down here is full of oxygen, but if we were on another planet with a different atmosphere, there gaz would more adequate for combustion?
Since other planets are limited to the same elements we have, there are certainly other gases that could oxidize carbon compounds, such as fluorine or chlorine, but I would guess that it would be difficult for life to evolve under conditions that lack oxygen due to oxygen's need for a higher activation energy. In an atmosphere full of Cl2 or F2 gases most things would just get oxidized pretty quickly and life would get snuffed out before it got very far.
I remember wanting an adequate explanation and not getting for a while. Then I learned that fire is kind of emergent. What I mean is that it doesn't exist. Just like space, time and gravity. That thing you see and call fire is only the production of photons and the dancing of the fire happens because of the random increases in entropy that occur during the chemical reaction. In other words heat or temperature is just particles in motion (kinetic energy).
The only reason we notice something is happening is because the event (the thing we call fire) is localized and very influential.
I think the dancing can be more specifically addressed than just an increase in entropy. Since wherever the flame is, that is where the reaction is occurring, in other words where the fuel is colliding with oxygen. Once that localized oxygen is used up, the fuel has to go elsewhere to find oxygen, react with it, and produce light. Meanwhile air immediately fills the localized area the flame moved away from, and so the fuel can come right back again and react since there is now oxygen again at that once vacated spot. This is the dance. The increase in entropy is manifested in the dispersion of the products due to their high KE, as well as (usually) an increase in the relative amount of particles in the products compared with the amount of reacting particles, and since products are gaseous while many fuels are not, that would also increase entropy.
Thanks great explanation.
Grazie mio amico
I came here after a conversation about how to store my dad's oxygen tanks. I'd love to hear a better discussion about that with smarter folks.
I have been trying to figure out E=mc2 for the last few weeks. Its a mind-boggling assertion that mass and energy are the same thing.
So, I wanted to see how chemical reactions use this principle in everyday life. Your video is the only one I found that seems to connect chemical reactions and Einsteins equation. You dont outwardly say it, but you at least mentioned the idea that a gain or loss in mass will result in a gain or loss in energy to a system. Good enough for me. Thanks for the video!
Thanks for an interesting comment. I am not a physicist, but I have been interested in that same question, so I will briefly tell you what I have gathered over many years of reading.
1) The universe is made of energy of various forms. Energy is what composes our universe. However all those forms of energy are a combined kinetic energy and potential energy. That's it-- any form of energy has both potential and kinetic components combined.
2) kinetic energy (KE), the energy of motion, seems straightforward. However what is potential energy? The most accessible way to think about potential energy (PE) is that it is the potential to do something. In physics, it would generally be the potential to do work (move an object of any sort). In chemistry it is thought more specifically to be the potential to react, but this can broken down upon closer inspection as the ability to do work.
3) The law of conservation of energy is concerned with the energy of the universe-- it cannot be changed. The law of conservation of mass, however, is not a universal law. It is more localized to a specific chemical or physical process. We know that the amount of mass in the universe is changing all of the time via mass becoming other types of energy, or energy that is not mass changing into mass. Textbooks are now more often combining the two laws-- "the Law of Conservation of Mass-Energy" which I find annoying since it is confusing to students and unnecessary.
4) In a chemical reaction, mass is conserved. I did not mean to imply in the video that it is not, if that is what you got out of it. Rather, in chemical reactions energy can change form from PE to KE and vice versa. However this does not affect the mass. The reason for the KE-PE exchange is due to electrons changing position and allowing new bonds to become shorter (power PE) or longer (higher PE). In physics, PE is often considered the energy of position-- how far away two objects are will determine their relative potential energies. But the same goes for chemistry, except now it is A) the position of electrons relative to the nucleus, and B) the position of two atoms relative to each other, and in particular in a chemical bond. Electrons will have a smaller average radius in a lower PE atom than in a higher PE atom. Bonded atoms with a shorter nuclear distance (closer together) will have a lower PE than bonded atoms with a longer nuclear distance. In burning methane, the bond distances in O-O and C-H bonds are longer than they are in the product bonds of O-H in water and C-O in CO2. This is because the decrease in PE in the products comes from the valence electrons getting closer to their nuclei, and this allows for the bonded atoms to get closer.
5) I have often wondered how exactly PE can become KE, but I think it is akin to a spinning figure skater bringing her arms closer to her body resulting in a faster spin. It is simply conservation of momentum.
6) Finally, E=mc2. The above was all really an explanation of why E=mc2 does NOT apply to a chemical reaction (sorry). Mass-energy transformations are independent of electron behavior in atoms, which is what drives a chemical reaction. I like to think of mass as a very localized and hugely concentrated potential energy. That is how I finally was able to wrap my head around it. The potential energy changes that occur in mass-energy transformations of matter are nuclear (rather than chemical) changes. This is the basis for the sun's energy, atomic bombs, nuclear power plants, etc. It is a great source of energy, and extremely clean compared to burning fossil fuels. Nuclear changes involve the loss of small particles we call radiation (alpha particles are electrons, beta particles are helium nuclei, and gamma particles are photons), or using up energy via the strong nuclear force, which changes the mass of nuclear particles. The strong nuclear force is what overcomes the massive repulsion of adjacent protons, and this requires a massive amount of energy in turn, and that energy is taken from the mass of the nucleus, thus lowering the nuclear mass. I have no idea how the strong nuclear force takes mass from the nucleus, but we do know that if you add up all the independent masses of the electrons, protons, and neutrons that when combined make up an atom, that sum is larger than the mass of the atom, and that is due to this mass-to-energy transformation during the formation of the nucleus.
Hope that makes sense!
Man, I'm kind of disappointed I was wrong, but I appreciate you taking the time to clear that up. I just assumed that the energy release was coming from a drop in overall mass. So, chemical reactions are more about kenetic energy. Well, I need to do a lot more diving into this subject. But hey, I know more than I did yesterday, lol. Thanks for clearing this up!
You may want to read Einstein's explanation of it for the general reader-- Relativity: The Special and General Theory. I have not yet read it but I will someday!
Great video, i liked shared and subscribed to ypur channel. Do you think you can do one on why fire behaves diferent in gravity and in zero gravity?
It's a nice idea, maybe someday...
The flame goes up (away from gravitational pull) because it is composed of low density gases (the products of the combustion), or at least lower density than the surrounding air. Gravity pulls with more force on the surrounding air than on the gaseous products, and so the gaseous products go up. When those gaseous products form they produce light (the flame) and so we see the flame going up. Without gravity, there is nothing to guide the direction of the gaseous combustion products, and so they go in all directions simultaneously. With gravity, It is that density difference that shapes the flame, however with no gravity the flame is completely spherical.
Thanks
תודה שצפית
I'm honestly glad to know that there's an actual reliable way to get rid of methane.
Not sure if you're serious.... The result of burning methane, which is carbon dioxide (1:1 stoichiometric ratio), just adds more greenhouse gas to the atmosphere. Burning methane is not a good thing. I know methane itself is a greenhouse gas, and there has been a lot of media purporting that methane is a more potent GHG than CO2, but that is not the case. CO2 has greater warming potential than CH4. CH4 gets a lot of press in part because its release into the atmosphere is rising much faster than CO2 in the last several decades. CH4 is bad, definitely, but CO2 is worse.
@@CrashChemistryAcademy I'm only saying that because I'm pretty sure that methane is way harder to get rid of.
The environmental half life of methane is about 9 years versus about 100 years for CO2. So if left alone, methane will cycle out of the atmosphere about ten times faster than CO2. A large part of the difference is that the carbon in CO2 is fully oxidized, whereas the carbon in methane is not. This makes methane more reactive and more subject to environmental degradation as well as faster cycling through the earth's carbon cycle.
Very nice ex.
Really nice explanation! The molecular explanation is very helpful. Could you comment on why the fuel needs to reach its ignition temperature for the oxidation reaction to occur? What does that additional heat do at the molecular level, without which the oxygen won't acquire the hydrogen from the methane? Thanks again!
Great question! The bonds all require a specific amount of energy input in order to be broken. This is called bond energy. The added heat provides this required energy primarily via kinetic energy. The heat makes the molecules move faster, and so they collide with more force. If the collision happens with enough force, unstable (high potential energy) bonds will momentarily form (creating what is called an activation complex), which will then break the bonds that result in allowing it to go to a lower potential energy.
Thanks! That's really helpful. This also helps with my attempts to understand the differences (to the degree there are any,) between piloted ignition and spontaneous OR auto-ignition. Everything I read has the consistent refrain of 'the ignition temperature is the point at which the mixture will ignite'. The circular reference is very frustrating. It sounds like you're providing me with a better molecular definition of the term 'ignite'. Or maybe there is still something more about the magic moment of ignition that's eluding me.
If 'ignite' refers to processes that occur at a specific level of kinetic energy (in a viable mixture,) then as best I can discern, the only difference between auto-ignition and piloted ignition is that auto-ignition occurs when the kinetic energy in the mixture is sufficient to engage the process you describe above. Piloted ignition appears to do the same thing, but only increases the energy in a localized area around the ignition source (I'll skip over all the stuff I've dredged up about diffusion flames and premixed sources,) and then the chain reaction carries it outward.
It's been years since I took basic chemistry and I'm on a quest to really understand the molecular basis of fire. I've spent a lot of time reading on the internet, but your video did a great deal to really help me. Thank you for you clear explanations and the time you've invested!
I think the best way to look at spontaneous ignition, or any spontaneous reaction, is that they are not really spontaneous. Any reaction requires a minimum amount of kinetic energy to occur. However, our experience with what is called spontaneous reactions are reactions that occur at room temperature. Room temperature is about 295 degrees above absolute zero (both centigrade and Kelvin), which is a great deal of kinetic energy. Temperature measures the average kinetic energy of a system, and so anything at room temperature has a lot of kinetic energy. If that amount of kinetic energy happens to be enough for a reaction to occur, then it will proceed, and appear to be spontaneous. Many reactions of course require more kinetic energy than is provided by room temperature, and so we need to add energy to get the reactants to the required kinetic energy, at which point the reaction can then proceed.
Your reasoning is sound! There is a movement in chem education to focus more on particle behavior, which is the basis for chemistry, and part of that initiative may be simply the access to simulations/animations that were not available before.
Great illustration. One question: in thermodynamics the internal energy is all the vibration and translation energy of the molecules, and kinetic energy is the bulk motion...so when you say the potential energy is lower, do you mean the vibration energy is lower?
While you have asked a question that would likely take a few paragraphs+ to adequately address, potential energy of molecules can be described as concerned with the coulombic forces occurring between the particles that make up the molecule, in particular the positions of atoms within the bonding structure, the bonds themselves, and the positions of electrons relative to nuclei and other electrons. This view of potential energy excludes the kinetic energies of all the molecule's particles occurring by virtue of their movement, as opposed to their position relative to each other. So while internal energy includes the kinetic energy of all the component particles in a molecule (as well as potential energy), the answer to whether changes in KE plays a part in driving the reaction is probably yes, but the only way I can think of would be for those internal motions to be transferred to "bulk" kinetic energy, as you say. Food for thought, not entirely sure.
@@CrashChemistryAcademy Thanks for taking the time to respond. My confusion arises based on the fact that it is often stated that in a reaction like the one you have shown in the video, "enthalpy" of the products is lower. We know that enthalpy is u+p*rho, so assuming that pressure and density do not change significantly during the reaction, then essentially "u" or internal energy of the products is lower. But, we know that heat is released during the reaction, in other words the product molecules should be moving around much faster (highter temperature). How do I reconcile these two? Where am I going wrong? Your attention is much appreciated.
Sorry but it sounds like you know more thermodynamics than I do.... I do believe that when considering pressure in an open system, it is the external pressure on the system that is being considered, and so you are correct to assume that it remains constant within the course of the reaction. The sudden increase in KE and volume contributed by the products due to their becoming hot gases would have negligible addition to pressure and temperature of the surroundings in general. However if you define the surrounds as more immediate and/or the reaction as being very large, then the impact is not negligible, but that would make measuring enthalpy changes extremely difficult. Hope that helps!
@@CrashChemistryAcademy Thanks for you time. I should investigate this further :)
Hi There, I LOVE YOUR VIDEOS. Just thought I would throw that in!! Quick question... theoretically, could one use a different oxidizing agent than O2 and could there be a fuel that did not include hydro-carbons?
Thanks much! And great question, and yes! There are a few strongly oxidizing agents that probably would create reactions similar to combustion, in particular F2 and Cl2 are strong oxidizers. However most strong oxidizing agents act by releasing oxygen to the reducer, for example potassium chlorate and potassium permanganate and hydrogen peroxide all oxidize by giving up oxygen to the other reactant. A fuel is really just defined by how quickly it will oxidize, in other words is the reaction fast enough to release the heat we associate with burning. For example most metals will burn if given enough activation energy, or in particular if they are powdered. Powdered aluminum, powdered zinc, powdered iron, and powdered magnesium are all quite flammable.
@@CrashChemistryAcademy Thank you for the thorough explanation. Theoretically if something cannot combust but enough energy in the form of heat is added would it simply hit its melting point? Can all elements reach a level of energy of becoming vaporized?
Most if not all matter can exist as a solid, liquid, or gas, given the right conditions. Many substances with very high melting points will combust before melting, so if the heating is done in an inert environment then both melting and vaporizing can occur. An interesting example is the old incandescent light bulb, which gives off light by forcing a current through tungsten, which is not very conductive, the result being a lot of heat (and light) generated, which in air would create a combustion, but the tungsten is inside a bulb in an environment of argon, not air, and so no combustion occurs. So with even higher temperatures the tungsten would eventually melt and then vaporize.
@@CrashChemistryAcademyI love how fascinating chemistry is. Thank you so much for breaking things down so clearly! I wish you were my professor!!!
@@291ayl Thanks for asking great questions!
So did I just learn that fire is essentially water moving at high speed?! 🤯
th-cam.com/video/aLoS8U-C5W0/w-d-xo.html
you forgot to draw the little hill which is to start a alkane combustion reaction in the form of a spark or a little flame. This is to create the radicals of which the electrons can oxidize to form water and carbon dioxide.
In terms of energy, the video is concerned with the enthalpy change, not the activation energy. Thanks for the idea-- I'll make a video concerning collision theory and activation energy. (At some point...)
hi,can you explain what light chemically is like we know our brain chemically makes images by the help of it, Electromagnetic radiation but my question is by itself what is LIGHT ? thank you.
Light is electromagnetic wave to which our eyes are sensitive. Every object radiates but only visible spectrum of electromagnetic is called light
Great explanation! I'm still a bit unsure how the increase kinetic energy comes about. Due to conservation of momentum, the net momentum of the system must stay unchanged. Therefore, if two particles are attracted towards each other and decrease their potential energies while increasing their kinetic energies, the net momentum must still be unchanged. When the two particles finally make a bond and stick together, it is clear that the kinetic energies must go somewhere although the net momentum does not necessarily increase. It is my reasoning that this energy goes into vibrational and perhaps rotational energy and due to equipartitioning of energy this added energy then dissipates into the kinetic energy of the system of bonded molecule (finally increased net momentum). Is this correct?
What a great question! I certainly agree that a reaction cannot violate conservation of momentum, but my background is chemistry, not physics. I'm not sure I follow your reasoning, but certainly equipartition cannot be disregarded due to any reaction occurring with such large amounts of particles. I cannot quite think of how momentum is conserved, but one thing you should know is that I simplified the reaction mechanism quite a bit for the sake of not getting stuck in the weeds in my quest to explain the derivation of heat. I wonder if the momentum of emitted photons is significant in overall momentum. If a more sophisticated understanding of the reaction mechanism helps, I would suggest reading "Reactions" by the physical chemist Richard Atkins, in which he details the ongoing chain reaction of many radicals that constitutes the combustion of methane (p. 30-32).
@@CrashChemistryAcademy Thank you for your reply. I was just wondering where do the increased molecular speeds come from due to the chemical reaction. I was picturing the atoms attracted towards each other like an asteroid would be attracted towards earth. As they approach each other their speeds increase. However, due to conservation of momentum the center of mass of the asteroid-earth system would not move (of course neglecting other objects in our galaxy). Similarly, although the two molecules or atoms in a reaction are attracted towards each other and gain speed while approaching each other, the combined center of mass of those molecules/atoms shouldn't move as a result. So the individual atoms/molecules gain speed, but the system does not.
Anyway, I gained a lot of information from the video and it still clarified many things!
i have a question how kinetic energy of molecular bombarding so that othet molecular get heated??is that kinetic Energy producufe harmonic oscillation and trasfer its oscillation to other molecules?i am Little bit confuse between kinetic energy with heat energy?if you get my point then explain it briefly 😍
Great Question! Briefly, KE is transferred during a collision: A higher KE molecule will transfer KE to a lower KE molecule when they collide. This is how heat flows-- the transfer of KE during collisions, which is called conduction. To get a more in depth view of this and of heat, please see my video on heat: th-cam.com/video/_5AZwrTkQNA/w-d-xo.html
I felt stupid for wanting to know how fire works down to the molecule. Obviously we all know what fire does, it burns, creates heat, and burns things. However, I would've never known that the kinetic energy released is in the form of CO2 and h2o. What's the molecular reaction to liquid h2o being thrown on the fire? I know it puts the fire out.. but how? Another question.. is it possible to isolate the h2o released?
Great questions! I have a video on one way of isolating water from fire, th-cam.com/video/aLoS8U-C5W0/w-d-xo.html.
There are two mechanisms for water putting out a fire. The first is that water prevents oxygen from getting to the fuel, and the second is that water cools the fuel to below its ignition temperature. Water has a great capacity to absorb heat (large specific heat capacity of 4.186 J/gK). One mechanism may predominate initially depending on the volume of water versus the size of the fire. For a small fire, like a candle, water blankets the fuel source and keeps it wet, so oxygen is prevented from contacting the fuel, but of course it is also cooled down quickly. For a large fire like a building with fire hoses spraying water into the building, there is so much heat that much of the water evaporates, but evaporation only happens when absorbing a lot of heat (very large heat of vaporization) so the fuel begins to cool to below its ignition point, as well as eventually prevented from contact with oxygen.
Now that you answered the question of what is fire, now I wonder: Can we calculate the potential energy of a certain molecule? What I mean is, the conclusion that methane and oxygen have high potential energy compared to CO2 and H2O is because fire occurs and the product molecules emit light and dissipate heat. So it's a conclusion based on observation, but can we theoretically tell if a molecule has high or low potential energy beforehand?
Usually (not always) potential energy can be correlated with bond energy. Bond energy is the amount of energy required to break a bond, and bond energies can be easily determined using enthalpies of formation. The lower the bond energy, the more likely that bond can be broken under a larger variety of (chemical, but some physical as well) circumstances. In other words, a greater potential to react. Potential energy in this context is more specifically referred to as chemical potential energy-- what is the potential that something will react under some given circumstances. Something with a high bond energy (N2 in particular comes to mind) requires a larger amount of energy input to break a bond, so a reaction is less likely. N2 has extremely high bond energy and is extremely stable. So, to answer your question... the temperature of a collection of molecules can be measured, and this temperature can determine the average KE of that collection through the use of the boltzmann constant. If we know the total amount of energy in that collection of molecules, the KE can be subtracted, giving the total PE, which you can divide by the total amount of molecules to get an average PE per molecule. I speak in terms of a collection because temperature is a statistical measure. Simply by how we define temperature, one cannot measure the temperature of a single molecule, but there are ways that physicists can measure the KE of a single particle with lasers-- lasers can measure the KE of a single particle, for example in experiments that attempt to get a particle to absolute zero.
@@CrashChemistryAcademy Wow! wasn't expecting such a detailed explanation, thank you
👍
May I ask why does potassium catch fire when it's thrown into water?
I know that potassium is a fairly reactive metal and it does explode in water
I would like to know how does the chemical energy (I think) convert to thermal energy so easily
There are two reactions here. The first is the reaction of K with H2O which results in the formation of H2 gas and aqueous KOH. Because K has a relatively low ionization energy, it rapidly reduces the water by donating its valence electron, which releases kinetic energy. The kinetic energy released is the thermal energy you refer to. Because this happens rapidly, a lot of H2 is generated in a short time. Heat in the form of rapidly moving H2 gas is released (more thermal energy). As that large volume of rapidly moving H2 gas bubbles out of the water it collides with O2 in the air resulting in the second reaction, H2 + O2 -> H2O(g) + KE and light energy. The light energy emitted is the flame (the burning H2 gas). Often, because so much H2 is being generated, its reaction with O2 becomes explosive, the energy released being primarily kinetic energy, which means the water vapor (H2O(g)) produced is travelling and expanding at a very high speed, resulting in a pressure wave that we perceive as a loud boom when it hits our ears.
Crash Chemistry Academy oooooo
Thanks for the reply :)
I am wondering what you mean by energy Crash Chemistry ? I am wondering about the particle or wave that we see from a flame or the sun and stars.. I cant see it being a particle. If it was; then something would be missing after the reaction. Also its speed would vary depending on the resistance. or wave just like the stone hitting a pond the repulsion of the moving atoms pushing the one next to it on and on. what do you think it is ?
@@7kennyg For us energy is defined as the ability to do work, which comes out of energy's base unit of kgm^2/s^2, where m = meter. kgm/s^2 is force and if you use force to move an object some distance m, then you have work, whose units are kgm^2/s^2, which is energy. This is not a very satisfying definition, in terms of defining energy. It works mathematically but it is not intuitive. The entire universe is made of energy, even the matter it contains is just a form of energy (Einstein, 1905). The amount of energy in the universe is absolute, it is unchanging, however its form can change. All matter has two forms of energy, potential (the energy of its position relative to some other matter as well as the energy inherent in the fact of its existence), and kinetic (the energy due to its own movement). In transformations occurring in chemical reactions, the total amount of energy the particles have at the beginning must be accounted for at the end. Usually, there is a change in potential energy, and so it must be accounted for by a change in kinetic energy and/or light energy. There is nothing missing after the reaction, since light can account for any deficiency in energy when accounting for PE and KE.
so the kinetic energy is the heat? is that because the molecules move rapidly through air and cause friction which then generates heat? or am i misunderstanding something
Great question! Heat is a transfer of kinetic energy. Kinetic energy transfer only happens in one direction, high KE particles transfer KE to slower KE particles when collisions occur, resulting in the slower KE particles speeding up (getting hot). So we experience the heat of the fire in two ways: 1) when the high KE water and CO2 combustion products collide with the low KE molecules in your skin, the KE transfer increases the skin molecules' KE which sends a signal to the brain (things seem to feel a bit warm there...); 2) high KE water and CO2 collide with low KE air molecules, transfer KE to air, the air warms up (higher KE), which again you feel if that warm air hits your skin. Of course the same with any object the high KE molecules collide with, such as a wall, the KE is transferred to the wall molecules and if you touch the wall its molecules transfer their high KE to your lower KE skin, and the wall feels warm, although it is only your skin's nerve cells that are telling your brain that your skin's molecules are increasing in KE. Perhaps we can think of high KE particles as "carriers" of heat.
So why alcohol (or any C.H.) wouldnt ignite on air with touching O2 ? What is the spark ? Energy ?
Great question. When molecules collide, they have to do so with enough force to break apart atoms in order for a reaction to proceed. Although the average speed of oxygen molecules at room temperature (~25 C) is about 1500 km/hr, that does not create enough force to overcome the bond strength of hydrocarbons. So kinetic energy must be added in any form to increase the force of collisions so that atoms break apart. Once new, high speed products are formed, those provide the energy needed to keep the reaction going.
@@CrashChemistryAcademy So if we see a flame, which has enough energy to make a reaction, we can say, that kinetic energy transformed to heat is lost very fast thru the distance ? For example, candle fire is about 1-2cm long, so after that, reaction looses most of the energy and the oxygen stops colliding ?
@@aleshiukas Hi KE products (CO2 and H2O) escaping, or getting far enough from the fuel to not influence the reaction, will lose KE as they collide with air molecules. In any molecular collision, the faster molecule will transfer KE to the slower molecule, the result being the high KE molecule moving slower and the slow molecule moving faster from a gain in KE. The original amount of KE cannot change, and so as the collisions spread over a larger area, the KE per molecule dissipates and so as you get further from the flame, the total localized increase in KE decreases.
I would say that the flame is the boundary where there is not enough hi KE fuel to react.
Question: When you burn wood you get CO2 and water but you also end up with black ash. What is that? Is it just left over wood that didn't completely undergo combustion?
Leftover carbon. The combustion of wood can take several routes, depending on the temperature of the combustion, the thickness of the wood, and the amount of oxygen present. There is often a "char" or black carbon left as a final step of burning, and some of that can be left if not enough heat/oxygen is around to turn it into carbon dioxide. A hotter fire would leave you with gray ash, which is primarily the many minerals contained in the wood and a source of nutrients for newly sprouting plants to use after a forest fire.
is there a scientific method to finding out which chemical reactions would release more energy. I know hydrocarbons are used in cars and our bodies use carbohydrates, but I would like to find a chemical reaction that has a high energy output without experimenting first.
The reason I'm asking is because I have this idea of making an autonomous robot that recharges it's batteries using chemical reactions. Kind of like the robots in the cartoon known as Futurama. I know you'll find more energy in gasoline then in any battery of equal mass but I have a problem with the idea of having loud and smelly engines indoors. I just don't think that product would sell very well on the market.
The amount of energy released from any reaction can be calculated from what is called the change in the enthalpy of reaction, and is calculated by subtracting the standard enthalpies of formation of each reactant from the standard enthalpies of formation of each product, each multiplied by their stoichiometric coefficient. You can find tables of standard enthalpies of formation on the internet, and they are often called heats of formation.
There is a tremendous amount of research going on with making more efficient and more powerful batteries, so you may want to look in the literature to see how unique your ideas are or if others are working on similar projects.
Also, batteries themselves generate electricity via chemical reactions inside the battery, and a rechargeable battery is simply one in which the battery's reaction can be forced to reverse by the potential energy difference of an external energy source, usually electricity. So it seems your reaction used for recharging would likely have to generate a current that is reversing the reaction in your battery. In other words, you would be creating a battery to recharge a battery, if I understand what you are proposing, but the reaction may be able to recharge the battery via released energy in some other way, which is what you would have to figure out. Sounds interesting!
You could also think about using water as the source of energy. You will have to separate the oxygen and hydrogen first and reacting them again in a process called fuel cells. You will be able to generate electricity and clean water again as your end product. The reaction can be carried out for life provided if you are not losing your starting water. This is the best way I think.
im still having trouble understanding the potential energy, how does bond energy actually convert to other energy?
Great question, hard to answer. One thing is how bond energy is defined, which is the amount of energy required to break a bond, meaning break apart the atoms. So the attractive force (coulombic force) holding atoms together is a potential energy, but that is not what bond energy refers to. Bond energy refers to the kinetic energy that atoms must gain in order to break free of that coulombic force, but breaking apart atoms is a positional change and so that changes their potential energy as well. But that really does not answer your question. In the context of the video, one of the reasons atoms will form new bonds (products) is because those bonds allow for an overall lower potential energy in the molecule. It has been seen experimentally that electrons in a lower potential energy state are actually closer (on average) than electrons in a higher potential energy state (a positional change). If the electrons are changing PE when they form new bonds, then Conservation of Energy requires that the energy difference be manifisted in some other place. Niels Bohr established the model of electrons emitting light energy equal to the electron's change in energy (1913) based on previous understanding of electron behavior. This is a basic part of how our universe works. But in an atomic rearrangement there are other potential energy changes to account for, and these differences are accounted for by changes in kinetic energy. I personally find this somewhat unsatisfying, but learning the mathematics of quantum mechanics is the only real way to begin to approach this problem, and physics (quantum mechanics) still is unable to fully describe the chemical bond.
thank you for the response to the question, but now i know i’m not on the level to understand this yet.
@@dangtiendung4766 This question IS the key to the arrow and you certainly ARE on the right level because you ask the right question and the answer given admits that it is hard. The most correct answer may lie in quantum theory but for now a possible classical answer is that in forming a water or carbon dioxide molecule the electron clouds of these resulting products get too close and into the molecular Repulsion range. They then rebound with tremendous kinetic energy. The fire, or explosion, must expand outward because that is where the fast moving products find the least resistance. It may also be possible that the heat generated within the initial ball of reaction is enough to further accelerate the products for a very short time, or cause a shock wave if it is explosive.
First!
Is there fire that dont use carbon and hydrogen?
Yes, but not something you would normally experience. Fire is RAPID reaction of oxygen with the fuel, which for people is primarily hydrocarbons, like methane (natural gas) or wax or gasoline (petrol) or alcohol. Oxygen will react with the vast majority of elements and compounds on earth, but typically it is a slow, unnoticeable reaction giving off little heat and no flame. However, under favorable conditions it is usually easy to get things to burn, such as powdered metals like iron or aluminum or zinc (due to their high surface area), or with enough activation energy, for example the heat we supply to the gas coming out of our stove to get it to light. The gas would not burn without that added energy to get it going.
So fire makes water?
So if fire is producing water, then why it doesn't gets extinguished on its own??
Water in its liquid state extinguishes a fire in two steps-- 1) it prevents oxygen from getting to the fuel, and 2) it cools down the fuel below its ignition temperature. Without step two, once the water boils off the fuel would immediately reignite. The water produced in the fire is a gas (water vapor), not a liquid, and is produced at such high kinetic energy (high temperature) that it immediately shoots away from the fire, away from the fuel.
@@CrashChemistryAcademy thanks for explaining 👍
Fire is higher energy to lower energy. Okay. But what do you mean by higher potential energy ? I understand gravitational energy which is intuitive but I don't understand "molecules higher energy". What is stored ? How it is liberated ? And why is it liberated ? Why do we have to initiate by a fire (bc it doesn't start without) ? That's what bother me. A formula, higher to lower and tadaaa it's fire. But it's a description (A good overall one) but not a complete explanation. You just substitue fire by higher to lower energy (which cause kinetic + light), but didn't say about what is exactly energy potential. Could you add some details ? Thanks
The potential energy referred to is often called chemical potential energy, which is the potential of a chemical substance to undergo a chemical reaction and transform into other substances. Energy is liberated due to atoms rearranging or electrons transferring, resulting in a more stable arrangement of atoms and/or electrons. That liberated energy takes the form of kinetic energy and/or light. In the video's example, the methane (or any fuel) is in a chemical state (referring to atomic & electron arrangement) that has the potential to become more stable, in other words go to a lower chemical potential energy-- go to a state that has less potential to undergo a reaction. There has to be some pathway for this to happen, and oxygen, which itself has high chemical potential, provides a path to get to a lower chemical potential energy by allowing for the rearrangement of atoms & electrons into lower chemical potential energy. Batteries, food, and gasoline all have large chemical potential energies, which will get reduced when we use the battery (electron change), or eat the food (digestion), or burn the gasoline (combustion). In the case of batteries, the liberated energy is transformed into electrical potential energy, and in the case of food digestion the liberated energy is transformed into a different high chemical potential molecule called ATP.
Much of this is often described in terms of breaking & making chemical bonds, which requires an input or output of energy.
I'm sorry but it seems to me as if you've failed to address both the ignition stage of the reaction, and the fact that the reaction between the methane and the oxygen does not spontaneously occur at standard temperatures and pressures, but requires the fuel mix to undergo endothermic pyrolysis at a critical temperature for the methane and oxygen molecules to decompose before they can recombine in the exothermic oxidation reaction. The net exothermic heat that is a product of the oxidation reaction minus the endothermic pyrolysis reaction then in turn creates a chain reaction whereby some of the exothermic heat released from the oxidation reaction can then be employed for the endothermic pyrolysis of fresh fuel that allows the fire to keep going until the fuel runs out. So your reaction formula should really include both the ignition heat that starts the reaction, the combustion heat released from the oxidation reaction, as well as the feedback heat to further the reaction. It should also be mentioned for the sake of completeness that very often the oxidation reaction does not complete when carbon monoxide is the byproduct of the oxidation reaction. Methane is perhaps the simplest reaction to depict combustion for - a log on the fire is much more complicated because wood is composed of a number of different compounds, more so when it is green and wet. Do you have a video on just what the flame is composed of and what makes up the colors we see?
Yes I would agree, this is all overly simplified, but my aim was to get across to introductory chem students some ideas about how stoichiometric ratios give us an indication of how a reaction may proceed, what composes the heat coming out of a flame, what the flame is, how we can incorporate conservation of energy into a reaction, and the importance of hydrocarbon combustion in our lives.
I may have chosen the wrong reaction to talk about a reaction mechanism, since methane combustion is quite complex and does not follow the stoichiometry supplied by the coefficients. This is nicely explained in the eminent physical chemist Peter Atkins' book "Reactions: The Private Life of Atoms" (2011), chapt 3, pp 29-32. Introducing pyrolysis would have been beyond the scope of the video.
However, introducing energy of activation certainly would have been within reach, but I decided to make a separate video for that, which is forthcoming (waiting 'til May, my retirement, to get back to making videos...). More specifically, pyrolysis in hydrocarbon combustion certainly is a good topic, and I agree, had I mentioned activation energy I certainly would have included the heat feedback to the reaction. I thank you for some good ideas for future videos!
I just wanna know why my motorcycle is so fast 😂
Since you asked...
Gasoline is a hydrocarbon, so when gas is burned in the engine's cylinders, it produces two gases, CO2 and H2O vapor. The gasoline is to a large degree vaporized by its injection into the cylinder at the point at which the piston has reached its maximum closing of the cylinder's space above the piston. That vaporized gasoline vastly increases its surface area compared to liquid gasoline, meaning there is far more contact with oxygen in the chamber, and so when it is ignited in the chamber, the burning occurs at an extremely high rate-- it only takes a moment for the injected gas to react with the oxygen. The result is an extremely rapid production of the CO2 and H2O vapor products, which are produced with very high kinetic energy-- those molecules are traveling and extremely high speeds, and because of 1) the production of a large amount of gaseous molecules in a very tiny amount of time, and 2) their very high speed, the result is a very large sudden force from gaseous particles hitting the surface of the piston and pushing it down, a force that is translated to your wheels via the crankshaft. The crankshaft being the essential link of translating the linear motion of the piston to rotational motion used by the wheels.
wait, so the heat from a flame comes from fast particles and not black body radiation?
One way to look at it is black body radiation would be emitted in all directions, however we only feel heat primarily above the flame, due to the buoyancy of the hot gaseous products. Whatever black body radiation is coming from the molecules in a combustion is likely not in an energy range that will be absorbed by the skin, but even if it was absorbed, its effect would be quite small compared to the conduction occurring through skin colliding with high KE molecules: molecules either from the reaction itself, or from air heated by collisions from the high KE reaction products. The light of the flame itself is not black body radiation, the molecules in the flame are probably a few hundred degrees below the temperature needed to begin releasing visible (red) light. The visible light of the flame comes from valence electrons losing energy. To reach the very beginning of the red range in black body radiation, about 800+ kelvin is needed, but that would not be from a flame, it would be from an object that is at 800 K.
@@CrashChemistryAcademy Great explanation, thank you!
You’re welcome!
I have a doubt that we have only 21% of oxygen in atmosphere so how can we perform complete combustion or else is not possible ?
It is unusual for combustion to be complete in normal atmospheric oxygen.
your skin feels heat primarily through intense infrared radiation not the kinetic energy of water vapor or co2 molecules … the combustion youre dealing isnt the same type of combustion used to power machines etc
You are conflating two separate sources of light. You are speaking about black body radiation, which is produced by nuclear vibrations, not electrons. The light in methane combustion is emitted by electrons, and it is not IR. Yes it does emit IR, due to its temperature, but that is a separate consideration from the actual reaction, which occurs though a change in electron location/electron energy. (See heat and IR below). I have not investigated other combustions, and since IR is just below red, it seems likely that IR would be emitted by electrons in other combustions. Black body radiation (= nuclear vibration) hits the visible (red) at a bit beyond 800 K. The temperature at which the products are produced in a simple methane combustion is not high enough to get to the visible range for black body emission, however an increase in oxygen concentration would increase the reaction rate and so certainly would increase the temperature of reaction products. And certainly any fire whose products are above that 800+ K temperature will be emitting light in the visible range through black body radiation.
Regarding heat and IR, I repeat my simple previous reasoning: If IR, which is emitted in all directions, were the primary carrier of heat in a fire, it would be felt in all directions, which it is not. The reason heat is so much more intense above a fire than around or below it is simply due to the buoyancy of the high speed expanding gaseous products being forced upward by the more dense air around it. Molecules are extremely efficient at transferring KE due to conservation of momentum, and so those high KE combustion products increase the skin's KE, and thus its temperature, quite efficiently. You may want to more thoughtfully consider the differences between 1) black body radiation, 2) light generated by electrons, and 3) heat transfer via conduction.
But why does water have lower potential energy? If anyone can answer this, I'd really appreciate it
The valence electrons in the two bonds are closer (on average) to the H and O nuclei than they are in most other bonds. This makes the molecule more stable, less likely to react, meaning a lower chemical potential, which is a lower potential energy.
@@CrashChemistryAcademy I just find it weird how something being more stable means that it'll move faster. That's the part that's unintuitive to me.
Thank you for addressing my previous question.
@@voldy2189 Stability refers only to potential energy, in other words the potential to react (chemical potential). KE is always integral to a reaction, and you can think of it as what is the potential for something to react at a given KE. Low PE means it is less likely to react at that KE than something at a higher PE.
@@CrashChemistryAcademy I understand the potential energy part of it. I just don't understand how that effects the speed that water moves. Like in the situation in the video, we have methane and oxygen reacting to make water and carbon dioxide. Since water is more stable(has lower PE) than the reactants, it moves faster(has more KE).
But why? Like I understand conservation of energy is necessary but typically that conservation is intuitive. Like when Potential energy is converted to Kinetic energy it's like a ball sitting on a hill and then rolling down it. Okay. That makes sense. In this situation, what propels the water? What makes it go faster? It just seems weird that it's ability to react at a given KE would influence the speed of it at all.
Thank you again for taking the time to answer my questions. It was very unexpected haha
@@voldy2189 Intuition can be misleading. Scientists often rely on intuition that comes out of experience in the laboratory (or life), but the intuition has to be verified through experimentation. Much of science is not intuitive, especially in the science that underlies the high tech in which we embed out lives more and more. A different perspective on KE might help: When you experience a flame, you feel heat. We can simply say the heat is part of conservation of energy: reactants --> products + heat energy, and the total E of reactants = total E of products + heat energy. That heat is high KE particles. If any other form of heat is emitted, it would be infrared, but there is no infrared produced in methane combustion. When we feel the heat of the flame, we are experiencing the high KE products colliding with our skin and transferring that KE, and therefore increasing the KE of our skin. Nerves close to the skin surface detect that increased movement of skin molecules resulting in our brain telling us our skin is warming. Hope that helps!
ironic that fire generates water and CO2, two chemicals that put out fire
I wonder if water and CO2 are very inert chemicals (which is why they put out fire), photosynthesis must generate more energy per molar mass than ordinary fire to carry out chemical reactions with such unreactive substances. So why don't plants disintegrate? Why don't we copy that photosynthesis machinery to generate more energy?
Great questions! Yes water and CO2 are very inert. They have very low potential energy, which in chemical terms means they have little potential to react with anything, and that is exactly why they put out fire, but most explanations put it that they both smother the flame, which means they prevent oxygen from contacting the fuel. Water does more than that, however, it absorbs a large amount of heat, and so the fuel temperature is lowered below the point of ignition.
Not sure about energy per molar mass of CO2 and/or water if that is what you are referring to. You could look up the heats of formation of the two molecules and compare that to the amount of energy absorbed in photosynthesis. The energy generated by photosynthesis is about 1-2% of the sunlight hitting a leaf, however, given that only red and blue wavelengths are absorbed by chlorophyl, it is really far higher than 1-2% if just accounting for the amount of absorbed light in the required wavelengths. By "energy generated," I refer to the chemically stored energy from converted sun energy, energy stored by the plant primarily in glucose and ATP, as well as a couple other molecules. This stored energy is then used chemically in the large array of biochemical pathways of the plant, including 1) reducing the CO2 in the photosynthetic pathway (Calvin cycle), which takes quite a bit of energy as you alluded to, however far less than one would need just from calculating heats of formation. This is due to the catalysis of the enzyme rubisco dramatically reducing the amount of energy that would otherwise be required. And 2) the oxidation of glucose, which produces CO2 and H2O, which diffuses out of the leaves, so it all comes full circle. But these are slow reactions all enzymatically catalyzed, so the energy changes are slow, step by step, and that is why the plant does not disintegrate. Burning glucose in the open air releases the same amount of energy (and a similar amount of energy to burning any hydrocarbon), but at a far faster rate, so more energy released per unit time compared to the plant. All living organisms (well, 99.9%), oxidize glucose as their main source of chemical energy. And for added measure, rubisco is by far the most prevalent enzyme on earth.
Lastly, scientists have been trying to mimic in the laboratory photosynthetic reduction of CO2 for decades without success, or at least not successful in any energetically favorable way. If they were successful, it would go a long way toward reducing the amount of CO2 in the atmosphere.
@@CrashChemistryAcademy Thank you very much, then the energy per mass in theory is greater, but it lasts much longer than in a common flame, therefore there is no destruction of the plant cells and the enzyme that I mentioned drastically reduces the activation temperature, therefore it does not occur. extreme temperatures
thank you so much