The Equilibrium Constant & Gibbs Energy (HL) (DP IB Chemistry)

The Equilibrium Constant & Gibbs Energy

How is Gibbs energy related to the equilibrium constant?

• The equilibrium constant, K, gives no information about the individual rates of reaction

  • It is independent of the kinetics of the reaction

• The equilibrium constant, K, is directly related to the Gibbs energy change, ΔG^Ꝋ, according to the following Gibbs energy equation:

ΔG^Ꝋ = -RT lnK

• ΔG^Ꝋ= Gibbs 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, and Gibbs energy change, ΔG^Ꝋ, can be used to determine whether the forward or backward reaction is favoured

The relationship between the equilibrium constant, K, and Gibbs energy change, ΔG

• 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

Free Energy & Equilibrium Calculations

• The relationship between Gibbs energy change, ΔG^Ꝋ, temperature and the equilibrium constant, K, 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