Determine H° for the following reaction.?

Question

Determine H° for the following reaction.
N2H4(l) + 2 H2O2(l) N2(g) + 4 H2O(l)

You are given these data.


N2H4(l) + O2(g) N2(g) + 2 H2O(l) H° = -622.2 kJ
H2(g) + 1/2 O2(g) H2O(l) H° = -285.8 kJ
H2(g) + O2(g) H2O2(l) H° = -187.8 kJ

Answer 1

This is like the other one, but easier.

Start with the first equation you're given. Reverse the 3rd equation and multiply it by 2 to get 2 H2O2 on the left. Take the 2nd equation, multiplied by 2 to get rid of all of the H2 and O2.

Add them up and you're done.