The standard enthalpy of formation $$\Delta _fH^o$$ at 298 K for methane, CH₄(g), is –74.8 kJ mol^–1. The additional information required to determine the average energy for C – H bond formation would be :

The enthalpy changes for the following processes are listed below :

Cl₂(g) = 2Cl(g), 242.3 kJ mol^–1
I₂(g) = 2I(g), 151.0 kJ mol^–1
ICl(g) = I(g) + Cl(g), 211.3 kJ mol^–1
I₂(s) = I₂(g), 62.76 kJ mol^–1

Given that the standard states for iodine and chlorine are I₂(s) and Cl₂(g), the standard enthalpy of formation for ICl(g) is :

Phosphorus pentachloride dissociates as follows, in a closed reaction vessel
PCl₅ (g) $$\leftrightharpoons$$ PCl₃ (g) + Cl₂ (g)
If total pressure at equilibrium of the reaction mixture is P and degree of dissociation of PCl₅ is x, the partial pressure of PCl₃ will be

The equilibrium constant for the reaction
SO₃ (g) $$\leftrightharpoons$$ SO₂ (g) + $$1 \over 2$$ O₂ (g)
is K_c = 4.9 $$\times$$ 10^–2. The value of K_c for the reaction
2SO₂ (g) + O₂ (g) $$\leftrightharpoons$$ 2SO₃ (g) will be :