6.4 Hess’s Law

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Hess's Law Problems

Calculate ΔH° for the following reaction.

3NO(g) → N2O(g) + NO2(g)     ΔH°rxn = ?

THERMODYNAMIC DATA
2NO(g) + O2(g) → 2NO2(g) ΔH° = -113kJ
2N2(g) + O2(g) → 2N2O(g) ΔH° = +163kJ
N2(g) + O2(g) → 2NO(g) ΔH° = +181kJ

Calculate ΔH° for the following reaction.

C2H4(g) + 6F2(g) → 2CF4(g) + 4HF(g)     ΔH°rxn = ?

THERMODYNAMIC DATA
H2(g) + F2(g) → 2HF(g) ΔH° = -537kJ
C(s) + 2F2(g) → CF4(g) ΔH° = -680kJ
2C(s) + 2H2(g) → C2H4(g) ΔH° = +52.3kJ