8.57

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Liam Maxwell 2E
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Joined: Fri Sep 29, 2017 7:07 am

8.57

Postby Liam Maxwell 2E » Tue Jan 16, 2018 10:09 pm

I am extremely confused on how to approach this problem. Can someone please explain to me what clue in the problem allowed them to realize they had to write combustion equations for the individual components of the given equation.

Cam Bear 2F
Posts: 60
Joined: Thu Jul 27, 2017 3:01 am

Re: 8.57

Postby Cam Bear 2F » Tue Jan 16, 2018 10:31 pm

You have to write combustion reactions because you are given . The subscript c tells you it is for a combustion reaction.
After setting up AND balancing the combustion equations you use Hess's Law. Add up the three reactions to form the one you are solving for. If you reverse a reaction, you change the sign of the enthalpy. If you multiply a reaction by a coefficient, you multiply the enthalpy by that same number. To find the reaction enthalpy you add up all of the new enthalpies.

RyanTran2F
Posts: 44
Joined: Thu Jul 27, 2017 3:00 am

Re: 8.57

Postby RyanTran2F » Tue Jan 16, 2018 11:01 pm

In addition to Cam Bear's response, you can see that the question hints at you having to use combustion equation instead of one of the other 2 methods of solving for enthalpy since the book did not tell you to use a specific table or a page in the Appendix. This means you can only use what is given in the question so the only way you can do that is to use Hess's law with the combustion equations.


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