Hess' Law Cycles Involving Enthalpies of Formation

Two worked examples using Hess' Law cycles
F p-r

[@evaclarke2275]

I'd just like the say THANK YOU. I didn't understand a word of what my teacher was saying and I find it fascinating that 10 minutes of your teaching has made it all clear! I'm now getting all the questions in my hwk right! I really appreciate these videos!

[@lisalambdon1033]

Eva Clarke exactly the same here!

[@nihalshaji3702]

Same here

[@higgins2922]

This makes perfect sense now I've seen this video. Thank you so much! I'm definitely sharing your channel with all my friends

[@YusufKhan-ye7rp]

thank you so much bro I got my a level mock tmrw and had no clue what the hell hess cycles were you just saved my life

[@MaChemGuy]

GOOD LUCK!!

[@alishawarren4392]

Thank you so much! I was struggling a lot with hess cycles but you've explained it so clearly!

[@MaChemGuy]

Alisha Warren Glad you found it helpful.

[@watch_and_see3349]

out of all the youtube videos i saw, yours made me understand it!

[@akashhera]

Your explaination is great!

[@lmarie1999]

Such a good explanation!!

[@MaChemGuy]

Cheers for that!

[@lifechanging_edits]

Great vid!

[@ellenspencer1856]

bestie thank you so much this was the most helpful video ever, plz keep making more

[@MaChemGuy]

Ok, if you insist!

[@tarawaller9194]

Thank you so much! I actually understand the cycle now!

[@calax7147]

I don't understand for the first example why you would do +594 -882, why does the formation of SO2 become positive, I thought seeing as you are forming it, and bond forming is negative, you would do -594 instead and because you are also forming SO3, that would also be -882, how are you meant to know when the sign changes and whether something is bond breaking or bond making?

[@twilightselena4eva]

Really clear video, thanks!

[@QueannaJulien]

Very helpful and love that accent 😁

[@talhanumanan6029]

This was a great video and also helped me to do the homework Thanks a lot

[@melanie9142]

For the last question, you calculated 4 moles of nitric acid. Aren’t you only supposed to calculate one by definition? Definition of enthalpy change of formation is the change of enthalpy during the formation of 1 mole of the substance from its constituent elements. So we have to divide the final value by 4.

[@MaChemGuy]

The reaction does not represent the enthalpy change of formation for nitric acid.

[@cyberfood1352]

wow...best explanation ever

[@MaChemGuy]

Cheers!

[@sajjjid]

Hi Machemguy, I was wondering if you have any accompanying powerpoint for hess's law. I have to do a lesson observation on this topic in a few days time and have never had the pleasure of teaching it. Your videos are absolutely amazing by the way.

[@danielpedro2489]

wow, really helpful. i get it now

[@saadsalmankhan27]

Wonderful

[@mre9287]

So am I correct to assume that delta H of formation is basically product - reactants whereas delta H of combustion is the opposite, if so would it be plausible to just take this shortcut instead of going through the whole cycle thing?

[@lisalambdon1033]

This helped me so so much, thank you

[@jhanvibhimjiani1699]

hey this video was really helpful but i have a question.The definition of enthalpy change of formation is the enthalpy change when ONE MOLE of a substance in standard state is formed but in the examples above like the second example we have 4 moles of HNO3 so dont u like divide ur answer by 4 or something?

[@MaChemGuy]

I'm not calculating the enthalpy change of formation of HNO3 but using enthalpy changes of formation of the substances in the equation to calculate the enthalpy change for the reaction. Hope that makes sense.

[@jhanvibhimjiani1699]

MaChemGuy yes i understood ...thank uuu allloot :)

[@xyzgaming6347]

Can these elements directly form these reactants and products.ikr if you out sulfur and oxygen. Would it form sulfur dioxide?

[@ryansadler8625]

Dr. Davis Chemistry

[@nisargapoudel3911]

will they ever ask us to draw the hess cycle diagram or can we just use products - reactants ?

[@MaChemGuy]

Cycles are rarely asked for. If it’s not mentioned, p-r is fine

[@olih322]

Thank you so much this helped a ton!

[@MaChemGuy]

You're welcome!

[@sheev9852]

SOOOOOOOOOOOOOO Useful

[@fahmidababul9747]

sir will the enthalpy change always be -ve for formation/combustion? Many thanks for your help!!!

[@slystriker2535]

Thanks! This really helped

[@MaChemGuy]

Sly Striker Thanks for that. Glad to hear it. 😊

[@koombaz]

THANK YOU SO FUCKING MUCH! YOU HAVE SAVED ME

[@lordfarquaad9887]

Thank you so much

[@chiamakaonu1594]

you are amazing ..
i love you !!!

[@pianoprincess8]

Hi thank you for your videos, they are incredibly useful!
One question- why are enthalpy formation values negative when forming bonds is endothermic and positive value?

[@MaChemGuy]

Breaking bonds is endothermic and making bonds is exothermic

[@pianoprincess8]

yes sorry i realise now-always get confused!

[@MaChemGuy]

Just not in the exam!!

[@caleb12001]

10k views, My man! :)

[@blackhearted1248]

I love you mate thanks a lot!!!!!

[@coklat121]

THANK YOU SO MUCH😄

[@yussifmumin472]

Is it important to write the actual elements instead of writing 'Elements'

[@fahimal-huq6867]

THANKS!!

[@Sheetal-bn1td]

Dhanyawad

[@Nethmi3]

thank you

[@Noor-sq5tm]

Hi..I know it's an old video..but can you please tell me why did you multiplied 4×33 in converting elements to 4NO2....and also why did you write 2x-286 in converting elements to 2H2O...overall video is amazing

[@MaChemGuy]

Hi - the enthalpy change values are all per mole of substance. If you have more than a mole of a substance in the equation you need to multiply by the number of moles (i.e. the balancing number in front in the balanced equation) Hope that helps :)

[@Noor-sq5tm]

Oh thank you got it...I mistakenly got that multiply sign as "x" the alphabet

[@i_am_gods_child]

i'm trying to figure our what brand of toy the little Queen in the corner is

[@MaChemGuy]

Happy Land People from Early learning centre 👍

[@amarachiii4827]

If enthalpy change of formation is enthalpy change when one mol of substance is formed from its elements in standard conditions why was the product 2SO3 and not SO3?

[@MaChemGuy]

The equation I'm calculating the enthalpy change for is not the enthalpy change of formation of SO3

[@kamelawad1446]

i want to know what are the elements

[@DheerajKumar-gf9vn]

Sulfur and oxygen

[@lnfernalGamingYT]

omg it's so simple yet my teacher turned it into the Riemann Hypothesis

[@MaChemGuy]

Piece of you know what!

[@peaChes_s]

I still don't get how the arrows work? The direction of arrows!?

[@MaChemGuy]

In this type of cycles, the arrows do not signify whether a process is exothermic/endothermic as in Born-Haber cycles. They simply link substances together e.g. elements ---> combustion products, elements --> compounds. Hope that helps

[@peaChes_s]

@@MaChemGuy thanks for explaining

[@junayednaim6768]

But how would you find the actual elements?

[@chandlerkenworthy3185]

It is given to you in exams. Or you can Google it

[@raphaelmhlanga5972]

Class this like

[@gelliondx6388]

Thanks a ton

[@MaChemGuy]

Thanks x 10^6

[@issayellow_fair]

🌟🌟🟢