Calculating K for HW 11.39

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Calculating K for HW 11.39

Postby 504594108 » Wed Nov 11, 2015 1:53 pm

Why does the solutions manual multiply the K from 2BrCl = Br2 + Cl2 and the K from H2 + Cl2 =2HCl instead of adding them? Plus, because Cl2 is in both equations, doesn't that mean there is some overlap with the two K values?

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Re: Calculating K for HW 11.39

Postby Chem_Mod » Wed Nov 11, 2015 1:59 pm

K values are multiplied when you have a series of reactions. This can be easily seen by remembering that K is the ratio of products over reactants.

A + B --> C: K1 = C/(AB)
C + D --> E: K2 = E/(CD)

Overall reaction: A+B+D --> E
Ktotal = K1*K2 = E/(ABD)

In summary, there are three manipulations you may do with K:
1. If you add reactions, you MULTIPLY the K's
2. If you multiply reaction by a coefficient, you raise K to that EXPONENT
3. If you reverse a reaction, you invert K to get 1/K because the products are now reactants and vice versa

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