Q1(g). Equilibrium-constant conventions

Answer in brief

Kₚ is dimensionless; molar ΔᵣG° has units J mol⁻¹. The numerical constant depends on temperature and on the written reaction.

Key points

• The exponential argument must be dimensionless. Define Kₚ=Πᵢ(pᵢ/p°)^νᵢ for ideal gases, rather than multiplying dimensional pressures.
• Its temperature dependence obeys dln Kₚ/dT=ΔᵣH°/(RT²). At a given temperature, changing equilibrium composition does not independently alter Kₚ.
• Multiplying every stoichiometric coefficient by m gives Kₚ′=Kₚ^m and ΔᵣG°′=mΔᵣG°. Reversing the reaction gives 1/Kₚ. Thus the reaction equation and standard state must be specified.