Hess's Law

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Maria Trujillo 1L
Posts: 47
Joined: Fri Apr 06, 2018 11:05 am

Hess's Law

Postby Maria Trujillo 1L » Sun Feb 03, 2019 9:28 pm

I understand that delta H is equal to the summation of all the changes in enthalpy when a reaction occurs. However, I am unclear how to do this on a problem that involves reactions. I'm unsure which textbook has this problem, but how would you solve the equation below:
3C(s)+S8(s) ----> C3S8(l)

I know that you have to make up 3 different equations with proportions, but I am unsure how you do that and how you solve. This was shown in my discussion, but it remains unclear.

Thanks in advance!

Posts: 62
Joined: Fri Sep 28, 2018 12:29 am

Re: Hess's Law

Postby 904936893 » Sun Feb 03, 2019 9:34 pm

I know in the textbook sometimes just the final equation is given and not the intermediate equations that must be be set up and manipulated to solve for the final equation, but I'm pretty sure for this class that the intermediate equations and their enthalpies will be given in the problem so that all you have to do is solve them out to get to your final equation and then add all the reaction enthalpies together. I hope this helps / makes sense.

Sophie Roberts 1E
Posts: 61
Joined: Fri Sep 28, 2018 12:17 am

Re: Hess's Law

Postby Sophie Roberts 1E » Mon Feb 04, 2019 5:27 pm

I saw a problem like this too, and was wondering if we can just use the enthalpies of formations for each of the compounds and use the equation:
Enthalpy of formation (products) - Enthalpy of formation (reactants)
Instead of doing Hess’s Law? Or will you get different answers?

Return to “Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)”

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