Question

What is the approximate ΔH in kJ for the following reaction as written:

2NH3(g) --> 3H2(g) + N2(g)

Careful, what kind of bond does the nitrogen molecule make?

I think it's -86, but I just want to make sure. Thanks in advance!

Answer 1

btw, bond energy is 389 for N-H, 436 FOR H-H, and 163 for N-N

Answer 2

Did you read the "be careful" part of the question? I think you have used N-N but the N2 molecules is NtriplebondN.
Using your numbers I end up with 80 kJ. I tried moving numbers around to obtain your value and could not duplicate it.

Also I looked up delta Hf for NH3 and it is about -46 kJ/mol or about +92 kJ for the reaction in reverse; i.e., the reaction shown. dHf values are more accurate so this is in the right ball park I think.