Gibbs Free Energy & the Equilibrium Constant (DP IB Chemistry: HL)

Gibbs Free Energy & the Equilibrium Constant

• The equilibrium constant, K_c, gives no information about the individual rates of reaction
  • It is independent of the kinetics of the reaction

• The equilibrium constant, K_c, is directly related to the Gibbs free energy change, ΔG^Ꝋ, according to the following (van't Hoff's) equation:

ΔG^Ꝋ = -RT lnK

• • ΔG^Ꝋ= Gibbs free energy change (kJ mol^–1)
  • R = gas constant (8.31 J K^-1 mol^-1)
  • T = temperature (Kelvin, K)
  • K = equilibrium constant
  • This equation is provided in section 1 of the data booklet

• This relationship between the equilibrium constant, K_c, and Gibbs free energy change, ΔG^Ꝋ, can be used to determine whether the forward or backward reaction is favoured

The relationship between the equilibrium constant, K_c, and Gibbs free energy change, ΔG^Ꝋ

• At a given temperature, a negative ΔG value for a reaction indicates that:
  • The reaction is feasible / spontaneous
  • The equilibrium concentration of the products is greater than the equilibrium concentration of the reactants
  • The value of the equilibrium constant is greater than 1

• As ΔG becomes more negative:
  • The forward reaction is favoured more
  • The value of the equilibrium constant increases

• The relationship between Gibbs free energy change, ΔG^Ꝋ, temperature and the equilibrium constant, K_c, is described by the equation:

ΔG^Ꝋ = -RT lnK

• The rearrangement of this equation makes it possible to:
  • Calculate the equilibrium constant
  • Deduce the position of equilibrium for the reaction

ln K =