Homework Help: chemistry

Posted by timmy on Monday, January 23, 2012 at 8:05pm.

Calculate the value of DHo for the reaction 2 CH4 (g) -> C2H6 (g) + H2 (g) given the following thermochemical equations:
C2H2 (g) + H2 (g) -> C2H4 (g) delta = – 175.1 kJ

C2H6 (g) -> C2H4 (g) + H2 (g) Delta = + 136.4 kJ

C2H2 (g) + 3 H2 (g) -> 2 CH4 (g) Delta = – 376.8 kJ

a) + 65.3 kJ
b) + 338.1 kJ
c) – 415.5 kJ
d) + 688.3 kJ
dont understand help!

chemistry - DrBob222, Monday, January 23, 2012 at 8:20pm
This is an application of Hess' Law.
You want to arrange the three equations given to obtain the desired equation.
Reverse eqn 3 and 2 and add i eqn 1. When you reverse an equation, change the sign of delta H.
If you follow my directions, see if you get the equation you want and add the delta H values (with changed signs). You should obtain one of the answers.
chemistry - timmy, Monday, January 23, 2012 at 9:41pm
65.3?
chemistry - DrBob222, Monday, January 23, 2012 at 10:19pm
yes

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