At 25°C, the following heats of reaction are known: 2ClF (g) + O2 (g) → Cl2O (g) + F2O (g) ΔH°rxn = 167.4 kJ/mol 2ClF3 (g) + 2O2 (g) → Cl2O (g) + 3F2O (g) ΔH°rxn = 341.4 kJ/mol 2F2 (g) + O2 (g) → 2F2O (g) ΔH°rxn = - 43.4 kJ/mol At the same temperature, use Hess's law to calculate ΔH°rxn for the reaction: ClF (g) + F2 (g) → ClF3 (g)

-108.7 KJ/mol

Explanation:

Hess's law state that in a multiple stage reaction, the enthalpy change is the sum of all the enthalpy changes.

2CIF (g) + O₂ (g) → Cl₂O (g) + F₂O (g) ΔH°rxn = 167.4 KJ/mol

2ClF₃ (g) + 2O₂ (g) → Cl₂O (g) + 3F₂O (g) ΔH°rxn = 341.4 kJ/mol

flip the above reaction

Cl₂O (g) + 3F₂O (g) → 2ClF₃ (g) + 2O₂ (g) ΔH°rxn = - 341.4 kJ/mol

2CIF (g) + O₂ (g) → Cl₂O (g) + F₂O (g) ΔH°rxn = 167.4 KJ/mol

2F₂ (g) + O₂ (g) → 2F₂O (g) ΔH°rxn = - 43.4 kJ/mol

add all the enthalpy change = - 341.4 kJ/mol + 167.4 KJ/mol - 43.4 kJ/mol = - 217.4

2CIF (g) + 2F₂ (g) → 2ClF₃ (g) ΔH°rxn = - 217.4 KJ/mol

ClF (g) + F2 (g) → ClF3 (g) = (ΔH°rxn = - 217.4 KJ/mol) / 2 = - 108.7 KJ/mol