The Second Law of Thermodynamics: Heat Flow, Entropy, and Microstates
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- เผยแพร่เมื่อ 25 มิ.ย. 2024
- What the heck is entropy?! You've heard a dozen different explanations. Disorder, microstates, Carnot engines... so many different wordings and interpretations! Really, they are all related, so let's go through a few different formulations of the second law and ways of interpreting it. It's hard to understand, but who doesn't like a challenge?
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Next time my mom asks me to clean my room I’m just going to tell her that I cannot, because I respect the universe and that the universe likes spontaneous entropy!
In fact, cleaning a room increase entropy in the universe faster than doing nothing.
@@pedrosabbi yep cause it takes more energy to organize than it does to leave it be 😂
@@pedrosabbiyes because the human doing so
@@JamezBnd007yeah something need a high entropy which is concious human mind to let the surrounding as a low entropy
Simply stated, entropy is the relationship between the temperature of a body and its heat content (more precisely, its kinetic heat energy). Entropy, S, is the heat content, Q, divided by the body's temperature, T.
S = Q/T
Stated another way, the heat, Q, stored in an object at temperature, T, is its entropy, S, multiplied by its temperature, T.
Q = T x S
That is it. The definition of entropy, as originally conceived in classical thermodynamics, had nothing to do with order or disorder. It had everything to do with how much heat energy was stored or trapped in a body at a given temperature. Think of it this way. If you removed all the heat energy possible from an object by cooling it down as far as possible (down to absolute zero), and then kept track of the heat you had to put back into it to bring it back to a given state, that amount of heat supplied divided by the final temperature in kelvin would be the entropy of that object in that state. The entropy of system is the average heat capacity of the system averaged over its absolute temperature.
Thank you Kimberly. I understand it thanks to your explanation.
the fuck are you talking about
Ooh..Thank You❣️👋🏼😌🇸🇪
Thank you!
This definition is only true for reversible processes and doesn't do much to explain the philosophical meaning of entropy.
Dave your material is so well well organized for class room work and tests
I just started watching your tutorial and it gives me joy......
I wish your educational channel will be well known......
I'm trying to understand entropy perfectly and man it's not easy
You are the best. Thank you for the work you do in creating these lectures!
I hope your channelwill be the best educational channel and will soon have a million subscribers!
trillion
came true about 4 years later lol
This is like the show " professor proton " from the big bang theory show that Sheldon is fond of. And am really really fond of ur work, its simple, efficent and quite enough to keep going with the topics. Thank you professor Dave🤩
Thanks, I'm doing a physics presentation on entropy, this helped so much!
this is the best video i've found on this subject seriously, thank you!!!!!
these thermodynamics videos came just in time :D thanks alot ❤
I understand it better thanks to your explanation!
You are amazing..... You made thermodynamics bearable...😊😊 Thanks..
The music is so inspirational for learning hahhaha and that little character :)
Hi, Dave, great explanations..
Your video makes me want to learn more about entropy! Wish I could take that course about it LOL...
Thanks dear David!
First time I understood this concept 😄.. . .and it was my first attending lecture on your channel and experience is just voww...
Really you are an amazing teaching.....
Love & Respect from INDIA 🇮🇳🇮🇳🇮🇳
Same bro🤣
What an explanation u give sir
For all videos i prefer you for chem concepts
Your explanation is so easy to understand 😌 Thabk you ❤️
This was a heap of help
Morning professor Dave !!
Entropy in a general state has nothing to do with order or disorder, it is simply energy is more likely to move from a concentrated or dense state to a less dense state, unless prevented by some barrier. The microstates are equally probably the macrostates are not. The Carnot engine is a ratio of work to heat flow which always is less than 1
people always seem to gripe over the entropy/disorder thing, and i don't fully get it. of course to simply say entropy is disorder is an absurd oversimplification, but to me a dispersal of matter is necessarily disorganizing. atoms stacked up neatly in a lattice, vs. atoms flying around randomly in a gas, order vs. disorder. of course this notion of entropy is limited and doesn't apply to heat engines, so maybe it's a semantic issue. but i just don't see how using the word disorder is specifically incorrect. i just see it as the word we use to get people's feet wet with entropy. then after that they learn all this stuff in this clip. then later, even more.
I just do not see it as disorder, but a greater possible configuration space unless prevented. It's like work and energy some use them interchangeably, and it does no harm as further along it will be better defined. Or the idea of chemical energy, mechanical energy, etc, when its really just kinetic and positional.
Besides that one issue, you make great educational videos. You have a way of simplifying and communicating that I envy.
thanks kindly!
I think what confuses people is the idea of micro-states and macro-states. People think of the greater number of possible configurations as being disorder. This really was not an issue in classical thermodynamics, but as you know developed with quantum mechanics, and somehow Shannons information theory entropy got merged with thermodynamic entropy, and they are indeed separate entities/functions. And the power of Carnot shows that you must reject heat at the same rate as input for the cyclic process, such that for all real world processes, an engine cycle must always have less work output to energy throughput. However we should not confuse the work with the energy flow. The energy flow is the heat flowing in and out of the engine, which gives rise to the expansion and contraction of the working fluid of the engine. What is confusing is we call it Carnot efficiency, when it is not about energy efficiency, it is a ratio about work output to energy flow, whereby work output will never be 1 in the real world, and be significantly less in most cases.
I disagree with the deck of cards shuffling for an increase in entropy. There is no change entropy.
Each card is a distinct entity unique to its peers. In other words, no 2 cards are exactly alike. So, shuffling the deck would not change anything other than the order of the cards.
I do concede that if we are strictly talking about the colors or symbols of the cards, then the shuffling would increase entropy. This is due to having multiple copies of indistinct entities in the system.
But there is information on the cards. When you purchase the deck it is organized by suit and number, so it is in a specific permutation. When you shuffle them, they can adopt any number of permutations. So there is a dispersal of information.
Very useful vid!
Thank you professor.
I was taught entropy is randomness... and i thought that's it. But this man has made me think harder
Nope, I good example is which has higher entropy a glass of water or a glass full of tiny ice cubes. If you think of disorder you would arrive at the glass with the ice cubes, but in reality the glass of water has higher.
That is one serious Lumberjack shirt! I approve!
also I do benefit here by this at the time, chaotic.
if it means anything I only paused once and rewinded one spot after watching this twice I have one page filled out with your diagrams and the microstructure was very tight at giving me a vision.
Have you heard of Deus Ex Mckenna, His channels first videos feature three amigos discussing there work that tabulate for their book. Many things they describe go farther than simply saying " the pencil of god pushes" they have about a dozen different ideas for that in every hour long Trialogue. MUCH of what they discuss they revolve around the thermal dynamic principals. The first episode provides you with background and instruction to take it with a grain of salt.
Sir, please can you make another video totally on entropy ?
My 87 lecture slides in under 8 minutes 😍. well organized btw. 100% efficient.
Ty dave your the best from the Philippines btw
On example1 ;
There is a case of tiny probablity where the shuffled deck of cards ends up at its initial indexed state. Since there is still a possibility for shuffled deck to turn up as serial as the beginning, I've considered "Probable to increase but no way to tell." as the first answer. Is there any apparent problem this way of reasoning or is it more accurate?
Yes. That probability is 1/(52 factorial), which is insanely improbable.
Hey Dave, thanks for the video, it was very well done, but I'm interested in your intro/outro music. Did you make it yourself, or what??
i did indeed! i make everything related to this channel.
It's very nice c: sounds like fun to play too!
Thank you thank you Thank you!! :)
is the lost in energy is due to the exces of heat or frictions and sound
Those Intro Music Brings me back my nostalgic memory I mean my cartoons
thank you
thanks man
how do we derive the equation at 3:33 ?
I would like to suggest a clarification regarding the Carnot cycle and the (mandatory) presence of the low temperature reservoir. The video is potentially confusing in this regard since the discussion digresses to the inefficiencies present in an internal combustion engine of an automobile. This aspect is really superfluous to the discussion.
The Carnot engine itself is a fully reversible cycle. However, in order for the Carnot engine to operate - the presence of the low temperature sink is still mandatory.
The presence of the low-temperature sink returns the working fluid of the Carnot cycle to its original state at the beginning of the cycle(state 1).
Without this step the Carnot engine cannot sustain cyclic(continuous) operation. The key here is the term "cyclic operation." This detail is crucial to the discovery of entropy and the identification of entropy as a thermodynamic state property. The last item I will point out is that the change of entropy for a cycle is always 0 since it is a state property(just like internal energy).
I thought you did a nice job on the description of the microstates.
Hope this helps.
thanks for the information!
i like your teaching
hey professor Dave, may the Lord Jesus Christ bless you. I've been using your videos for my Thermodynamics class here in the Philippines. You are a blessing!
That's why my earphones always end up to be tangled. Universe wants it to be.
I liked your approach to disproving the flat earth theory using sound logic and science... now if you could please do the "collapse" of the Twin Towers.
thank you! 5:12, alwasy :)
thank you professor jesus explains
I can't unsee it now
When the universe reaches maximum entropy, there will still be gravity. Weak, but potent.
Nice
Sir... the way of explanation was awesome... and sir....Do entropy decreases for a particular system.. like u mentioned cold to hot heat transfer can't occur.. .but in the comprehension example 2 dew condenses by the result of decrease in entropy....doess that mean entropy is going bavk to its constant value... ?.. do entropy decrease???
no, condensation results in a release of energy, so energy is dispersed, entropy of the universe increases
@@ProfessorDaveExplains thnk u sir.. got it...
Amazing Dave.... THANK YOU. Micro state explanations simplified beautifuly. Plz change ur intro tho still luv u
can someone pls explain why entropy decreases on stretching a rubber band?
Taking a wild guess but maybe because it stores energy? So, entropy is the dispersal of energy. Stretching a rubber band is the opposite of that?
It is not true, at 1:33, that a Carnot engine is 100% efficient, it is only the most optimal engine you can imagine, not 100% efficient
A Carnot engine can only be 100% efficient, if you can exhaust your heat to absolute zero. Which is impossible according to the third law of thermodynamics.
@@carultch Yes of course, or if you can bring heat from a source at temperature of infinity degrees celsius
What about a heater?
5:00
Sorry for the dumb question but is it wrong to infer that time travel backwards is not possible within our universe ?
No, that seems to be a sound inference.
dave refrigerator is the reverse of heat engine ??
hmm... i guess, in a sense?
Yes but by external work done means of using electrical power
Like the Seebeck effect and Peltier Effect.
That photo of the universe
Is it the same that nasa posted this year🤔🤔
if it weren't for all these videos id probably score a literal 12 points on the MCAT chem/phys section
you were too late for me. I now understand the concept a bit more but I'm out of the program.
Hero
Your video is really nice, but the end example is not so good. Lambert 1999 says that you can not did a entropy example with macro things, because they are not colliding or exchanging energy.
His article name is "Shuffled Cards, Messy Desks, and Disorderly Dorm Rooms- Examples of Entropy Increase? Nonsense!"
all just analogies to get the concept across!
1:32 The Carnot engine is 100%efficient. 2:58 even the Carnot engine can't be 100% efficient 3:40 The change in entropy for the Carnot engine is zero. I'm confused..
Hmm... it's possible I misspoke on the second statement, I don't fully recall but I think the Carnot engine may be a hypothetical engine with an efficiency that is unattainable in physical reality.
@@ProfessorDaveExplains The Carnot engine is an upper limit to the theoretical efficiency of an engine, for a given heat source temperature and a given heat sink temperature. In reverse, it can also be the upper limit for performance of a heat pump or refrigeration cycle, with a given temperature on both sides of the space to be heated or cooled.
The Carnot engine is considered impractical, but not impossible. It is impractical to make all four processes of the Carnot engine work out perfectly with no frictional losses, and with infinitesimal temperature differences only. It is also impractical to make an engine work with the Carnot cycle processes, when other processes are more realistic to implement in practice. Which is why we use Rankine, Brayton, Otto, and Diesel cycles for actual heat engines.
Was. There. A. Period. After. Every. Word. On. The. Teleprompt. ?.
I. Don't. Know. What. You're. Talking. About.
Institutionalised Dave Bamboozles.
If I make absurd videos about fake conspiracies, then will you will subscribe?
i thought entropy was like reaching the lowest energy level?
Professor or Jesus?
False idols.
Haha
both
An example of increased order, that even the cosmic death of the universe would find hard to dissipate - an iron atoms fused in stars will stay whole even at 0 Kelvin even when Universe has stretched so far that there isn't another atom of anything in its bubble of its event horizon. It will never break down to its lighter elements.
There are examples where Entropy just ignores no matter how we like to rationalize it.
Imo the statistical explanation of Entropy - ie describing it as tendency to disorder is so misleading (first of all it's subjective) and ignores plenty of exceptions, so that any scientists describing Entropy this way should be ashamed of him/her-self :)
Hello Dave, I am dissapointed in the quality of your explination. Me and my friend Johan Are not able to comprihend what the flip you are talking about!! 🥵
SO EASY MANN
Carnot machines are reversible. And do not have 100% eficiency.
Why making it difficult? Ought to be a better way to do this. Problem is not many are interested in this.
It doesn't get any simpler than this.
still doesn't explain why our atmosphere doesn't go into space
Try watching my tutorial on Newton's law of universal gravitation. Then all the rest of my physics tutorials. Then admit to yourself that flat earth videos are made by con men that don't understand physics.
@@ProfessorDaveExplains will do thanks.
Escape velocity.
@@kyleharry6758 Our atmosphere does go in to space, as a consequence of solar wind. It is a slow process, and won't be a problem within the lifetime of humanity, but it does happen.
Carnot engine is 100% efficient? Oh no.
Hello sir catudio ahahahahahahahs
The way you speak at the end of the video, please speak like that the entire video....
Teachers should not speak quickly. That's a horrible suggestion.
Not quickly, normally. Massive difference before and after the teleprompter. You also sound much more clear and better without it. Its just an observation nothing to get offended about.
I understand, but you must realize how unrealistic that is. I take a lot of time with my scripts to ensure that every concept is explained with the utmost precision. I choose every word very carefully so that the clip can be succinct and effective, unlike someone who is rambling off the top of their head in an unprofessional manner. That's why a teleprompter is an absolute necessity.
Copy all, thanks for the numerous videos you have and the time you take to create them. This is one of many you have that have helped me earn As in my chem courses.
You're very welcome, thanks for watching!
One of the worst decisions in physics, Representing anything with the letter S