This was really well explained however I'm slightly confused about how you work out what goes at the bottom of the cycle and the number of moles it has, could you explain it for me please?
Is it just me or are the cycles the wrong way round for the questions. For calculating the enthalpy of formation, he drew a combustion cycle and vice versa for enthalpy of combustion.
Hi there, what do you mean by "start anywhere on the cycle and add up the numbers" - i don't understand what numbers you're talking about? if you can clarify this. thanks!
Yes. You have the enthalpy values next to the arrows. Start anywhere on the cycle and add the numbers up until you get back to where you started from. Change the sign if you go against an arrow, keep the sign the same if you are going with an arrow. It should add up to 0.
Ohhh. i get it now! so for the first example, if you start from -234 and go up, then add -732 and go across, and then add +966 as you're going against the arrow, it = 0. this clears it up, thanks!
For calorimetry the question gives the temperature change in degrees Celsius, so do we not convert to this to kelvin? In the markscheme it's not converted to kelvin. Thank you
Hi. Yes you need to know the change in temperature. The change in temperature is the same whether it is in kelvin or degrees Celsius. However all temperature must be quoted as kelvin.
No, look at the data, if the data is about enthal0y of combustion then the arrows face down. Doesn’t matter what they ask for. The arrows are related to the data
So basically bond dissociation enthalpy is the energy required per mole to break the intermolecular forces of attractions between the gaseous compounds, like Cl2?
You purely go off the data they have given you. If they have given you combustion data then you draw a combustion cycle, if they have given you formation data then you draw a formation cycle. Either will allow you to work out enthalpy of reaction.
Sir I have a massive issue I need help trying to understand... if products have higher energy than reactants surely that means it’s exothermic as more energy is released when the product is formed than the energy required to break the reactants’ bonds? Yet the diagram is labelled endothermic?
@@HamzaKhan0711 because the delta T means 'change in temperature' even if you convert to kelvin the actual temp change is still gonna be the same eg 20 C to 26 C --> changes by 6 293 K to 299 K --> changes by 6
Thank you so much for the video! You made Hess cycle seem less scary and actually much easier to understand than from the textbook😁
My favourite videos for ENTHALPY.... Thanks so much for explaining the definitions and conditions so clearly!!!
No problem!
This is the one topic I never understood but this is so well explained and simple, I now finally get it. Thank you so much!
Hello, I was hoping if you could make a video on hardest calculation questions in chemistry. Thanks!
Thank you! your videos are live savers!
This was really well explained however I'm slightly confused about how you work out what goes at the bottom of the cycle and the number of moles it has, could you explain it for me please?
Is it just me or are the cycles the wrong way round for the questions. For calculating the enthalpy of formation, he drew a combustion cycle and vice versa for enthalpy of combustion.
how did you balance the numbers at the bottom of the enthalpy cycle I don't get that bit
What an amazing man.
Hi there,
what do you mean by "start anywhere on the cycle and add up the numbers" - i don't understand what numbers you're talking about? if you can clarify this. thanks!
Yes. You have the enthalpy values next to the arrows. Start anywhere on the cycle and add the numbers up until you get back to where you started from. Change the sign if you go against an arrow, keep the sign the same if you are going with an arrow. It should add up to 0.
Ohhh. i get it now!
so for the first example, if you start from -234 and go up, then add -732 and go across, and then add +966 as you're going against the arrow, it = 0.
this clears it up, thanks!
That's it! Pretty smart isn't it! Just a way of making sure your numbers are definitely correct.
For calorimetry the question gives the temperature change in degrees Celsius, so do we not convert to this to kelvin? In the markscheme it's not converted to kelvin. Thank you
Hi. Yes you need to know the change in temperature. The change in temperature is the same whether it is in kelvin or degrees Celsius. However all temperature must be quoted as kelvin.
Hi Chris,
in combustion cycles do you never count the enthalpy of combustion of oxygen?
at 22:36 did you mean this the 'enthalpy of formation'?? isnt it meant to be combustion due to our arrows facing down?
No, look at the data, if the data is about enthal0y of combustion then the arrows face down. Doesn’t matter what they ask for. The arrows are related to the data
this is SO. HELPFUL. thank you
Glad it was helpful!
19:05 Why is there only 1 carbon in elements for formation isnt there supposed to be 2 Carbons as there is one in methanol and one in carbon dioxide?
at 18:05, why did you use 1.5O2 rather than 3O2?
ik im like 8 months late but its cus he was balancing the equation
amazing thanks so much saving my mocks !!!
You're welcome 😊
You are the best❤
So basically bond dissociation enthalpy is the energy required per mole to break the intermolecular forces of attractions between the gaseous compounds, like Cl2?
no, the reaction given shows formation. but your given the units for enthalpy of combustion. meaning you have to follow the combustion route
Hi, what if you are given the values for enthalpy of reaction and need to find the enthalpy of combustion or formation? Which way do the arrows go?
You purely go off the data they have given you. If they have given you combustion data then you draw a combustion cycle, if they have given you formation data then you draw a formation cycle. Either will allow you to work out enthalpy of reaction.
@@AlleryChemistry Thank you!
habibi this video v good one
Hello sir just wondering for 9:36 where did 1662 come from I don't get it
Hey Chris, are these videos for the old spec or the new one?
For the calorimetry equation does temperature have to be in K?
it doesnt matter whether its in C or K...late reply huh XD
Love you ❤
This was super helpful thankyouuuu
Yr videos are amazing
or is the oxygen just used to balance the equations?
for q2 why is the temp not in kelvins?
Sir I have a massive issue I need help trying to understand... if products have higher energy than reactants surely that means it’s exothermic as more energy is released when the product is formed than the energy required to break the reactants’ bonds? Yet the diagram is labelled endothermic?
if the products have higher energy it means they've absorbed energy. that's why the diagram is labelled as endothermic
Thank you!
Legend
Don't we have 4 lots of C=O as each CO2 has 2 C=O bonds?
did you find the answer to this?
In the q=mc^T, temp is in K so aren’t you meant to convert into from °C to K but in the example you didn’t I’m confused
are you still confused?
@@anotheryoutubeuser1298 I am. Why isn't there a conversion to K from degrees celsius? When do you convert to K in the q equation?
@@HamzaKhan0711 it doesn’t matter for those type of questions
@@HamzaKhan0711 you do convert he just forgot
@@HamzaKhan0711 because the delta T means 'change in temperature' even if you convert to kelvin the actual temp change is still gonna be the same
eg
20 C to 26 C --> changes by 6
293 K to 299 K --> changes by 6
I get 50 for the Mr of ethanol
i love you
is this for AS level too?
yes its in module 3 and as level is from modules 1 -4
16:20
ur a fucking legend mate
Finally a method I can comprehend 😂. Thanks
Ayooo btecc