Question

What is the process to calculate ΔH° for the reaction?

O2(g) + 2NO(g) --> N2O4(g)

O2(g) + 2NO(g) --> 2NO2(g) ΔH°1

N2O4(g) --> 2NO2(g) ΔH°2


a) ΔH°1 + ΔH°2
b) ΔH°1 - ΔH°2
c) ΔH°2 - ΔH°1
d) ΔH°1 - 2ΔH°2

I know according to Hess' Law that I need to take the ΔH° products - ΔH° reactants.

I am a guessing it would probably be c.

Answer 1

To get equation 1 you want to add equn 1 to rhe reverse of equn 2. reversing eqn 2 makes it a minus dH2. Look to me like c is not right

Answer 2

So if it is the reverse of equation 2. You would have to take ΔH°1 - ΔH°2?

Answer 3

yes. Write out eqn 1 and add it to the reverse of eqn 2 and see if it give you the reaction you want.