We’re being asked to determine the enthalpy change (ΔHrxn) for the chemical reaction:
N2O4 → 2 NO + O2
We can use Hess’s Law to determine the enthalpy change of the overall reaction from the given reactions:
1. N2 + 2 O2 → N2O4 ΔH1 = −8 kJ/mol
2. N2 + O2 → 2 NO ΔH2 = 180 kJ/mol
We now need to find a combination of reactions that when added up, gives us the overall reaction.
Consider the following set of reactions:
N2 + 2O2 → N2O4 ,ΔH=−8 kJ/mol
N2 + O2 → 2NO ,ΔH=180 kJ/mol
The equations given in the problem introduction can be added together to give the following reaction:
overall: N2O4 → 2NO + O2
However, one of them must be reversed, reaction 1: N2 + 2O2 → N2O4
What is the enthalpy for reaction 1 reversed?
reaction 1 reversed: N2O4 → N2 + 2O2
Express your answer numerically in kilojoules per mole.
What is the enthalpy for reaction 2?
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