# Chemistry

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.

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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

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

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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.

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