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April 25, 2015

Homework Help: Chemistry

Posted by Steven B. on Sunday, October 31, 2010 at 12:26am.

A quick question. When we use the bond energies to find delta H, should we use the sum of the bond energies of the reactants minus the sum of the bond energies of the products, or vice versa?
For example, H2 + Br2 --> 2HBr
Given that
H-H bond is 436 KJ/mol
Br-Br is 193 KJ/ mol
H-Br bond is 366 KJ/mol
_____________________
So sum of bond energies for reactants is 436+193=629 KJ
and the sum of bond energies for the products is 2*366=732KJ
And my question is: Is delta H 629-732 or 732-629?

Thanks.

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