The standard enthalpy of formation of SO₃(g) is -395.7 kJ/mol. What is Δ H for 2SO₂(g) + O₂(g) → 2SO₃(g) if Δ Hf° (SO₂,g
Δ H = [2 × Δ Hf° (SO₃)] - [2 × Δ Hf° (SO₂) + Δ Hf° (O₂)] = [2 × (-395.7)] - [2 × (-296.8) + 0] = -791.4 + 593.6 = -197.8 kJ/mol.
Ref: NCERT Class 11 Chemistry > Chapter 5: Thermodynamics > Topic: Enthalpy Changes - Reaction Formation Combustion and Hess's Law