Hess's Law

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Hess's Law

Postby 204563981 » Sun Jan 10, 2016 5:55 pm

When using Hess's Law, how do you cancel pieces of the reactions that are intermediate?

Shrita Pendekanti 4B
Posts: 22
Joined: Fri Sep 25, 2015 3:00 am

Re: Hess's Law

Postby Shrita Pendekanti 4B » Sun Jan 10, 2016 7:00 pm

You should be able cancel out the intermediate terms by manipulating one of the steps in the process so that the molecule you wish to cancel is present in an equal number of moles on the opposite side of the reaction equation in some other step. This way, the terms cancel out when the steps are added together.
Reaction equations can be manipulated by either reversing the process (R-->P becomes P-->R and sign for delta H switches) or by multiplying each term (and delta H) by a certain value that will lend to the cancelation of intermediate terms (R-->P delta H becomes 4R-->4P with delta 4H)

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