How to Draw Energy Cycle for Enthalpy Change of Formation - Energetics

In this video we want to learn how to draw the energy cycle given enthalpy changes of formation of compounds and calculate the enthalpy change of a reaction using Hess' Law.
Let's take a look at this exercise.
DEFINITION OF ENTHALPY CHANGE OF FORMATION
In order for us to draw the energy cycle, we need to understand enthalpy change of formation and be able to write out equations to show the enthalpy change of formation of these compounds.
Enthalpy change of formation is defined as the energy change when one mole of compound is formed from its constituent elements in standard states.
For the balanced equation the coefficient of the compound has to be fixed at one since enthalpy change of formation is with respect to per mole of compound:
DRAW ENERGY CYCLE
Next we can draw the energy cycle by writing out the main equation first.
Since we are given the enthalpy change of formation of all the compounds, we can link this equation to elements in the standard state, which we can put below the main equation.
After balancing the elements, we can add arrows for each formation reaction.
First let's account for formation of SnO2. Since coefficient of SnO2 is 1, the enthalpy change of formation for SnO2 is unchanged.
Next for formation of CO. Since coefficient of CO is 2, enthalpy change of formation for CO has to be doubled.
Finally for formation of CO2. Since coefficient of CO2 is 2, enthalpy change of formation for CO2 also has to be doubled.
APPLY HESS' LAW
Once the energy cycle is complete, we can determine which of these arrows are clockwise and counter-clockwise.
Finally we can apply Hess' Law by putting all the clockwise arrows on one side of the equation and all the counter-clockwise arrows on the other side of the equation to solve for the unknown enthalpy change.
For the detailed step-by-step discussion on how to draw this energy cycle, check out this video!
Topic: Energetics, Physical Chemistry, A Level Chemistry, Singapore
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[@roriefriz9068]

OMG I LOVE YOU RIGHT NOW!!!! I'VE BEEN SOOO CONFUSED AS TO WHY THE HELL THERE ALWAYS WAS A 1/2 INFRONT OF THE O2 AND NOONE EVER EXPLAINED IT AND NOW IT ALL MAKES SENSE. thank you so so so much, please keep on doing what your doing you really helped me out here. Hours of frustration and its way clearer now, thanks so much again!

[@cesbon]

Just subsribed! Well explained sir. You've covered almost all the parts of this section just as my reference book but is more explanation and detail. Thank you so much sir!

[@luanhurter4547]

Wow, I actually understand. Thank you so much!

[@qiaoyilim8572]

thank you so much this video convinced me to hang on to h2 chem for a little while longer i hope you know how much of a difference you've made to me please never stop doing this

[@ChemistryGuru]

Hi Qiaoyi thanks for the kind words. Jiayou and keep fighting! :)

[@m3ronnn]

This was really helpful, thank you :)

[@nabilahhusna8092]

thank you! i understand more of my lesson after watching this vid :)))

[@patrecepascal5448]

This video was so helpful i didn't understand anything my teacher explained. thank you so much!!!

[@fatin4400]

Hi im student from malaysia..thank u so much sir for this useful video u help me a lot 😊👍

[@abdullahkhasawneh328]

my g, my fokin bruda, now i understand this :)

[@abigailsookdeo]

Thanks so much ! Really helpful

[@hassanjunaid6496]

I've got my Chemistry paper 2 tomorrow.. Cambridge exam... and I can't thenk ye enough fer dis vid!!!!🤗🤍
Dis vez sooo muchhhh helpful... Ye cleared all da doubts which I had had fer... like a whole year!!
Thenkssss a lot💫🙌🏻👏🏻

[@deepikafernando9414]

Thank u ...very useful video..cary on...😊

[@AJ-sd1fx]

thank you very much !!

[@shreekarimaruvada]

thank you for this!! im so much clearer on this topic:-)

[@ChemistryGuru]

Thanks Shreekari! Glad you found it useful 😄😄

[@christianpenguinss3708]

thank you so much for this!

[@mishaalirfan7483]

thank you soo much sir !

[@naveedhasan6738]

Thank You From Bangladesh

[@tamarazvarayi3955]

makes much more sense! thank you

[@ChemistryGuru]

Hi Tamara! Glad the video was useful :)

[@arpita6279]

thankyou so much

[@loksuriyaa_gamingyt1374]

thank you very much chemistry guru

[@ChemistryGuru]

you are most welcome! glad you found it useful! :)

[@suhaylahasan9985]

I love u sir

[@solehah.a7507]

Do you have explanation for Hess Law energy level diagram?

[@ChemistryGuru]

For energy level diagram you can check out this video regarding Born Haber cycle :) th-cam.com/video/KnnOCYAla18/w-d-xo.html

[@Kamen9954]

how about the hess's cycle of calcium hydroxide: ca+O2+H2--->Ca(oh)2, enthalphy change of formation of water is -286kj mol-1

[@roriefriz9068]

Why did you say we want to find the enthalpy change ΔH for SnO2(s) +2CO(g)--> Sn(s)+2CO2(g) and not enthalpy change of formation ΔHf? Could you say theyre the same in this case? Reallz appreciate the feedback you give and the amount of effort you put into your videos they really help!

[@usmanwaj1668]

yep same thing

[@virealsons8223]

hi, how to determine direction of arrow for (triangle)H

[@ChemistryGuru]

Formation is to form 1 mole of compound from its elements in standard state, so the direction of arrow for reaction will be from elements (reactants) to compound (products)

[@lolaxmed9046]

is this hess law

[@ChemistryGuru]

yes this is application of Hess law. drawing energy cycle and then finding enthalpy change of unknown using Hess Law.

[@AyeshaKhan-il5rs]

Thanks sir. But i have a question? Are you chinese