Chemical equilibrium and the equilibrium constant

Learning objectives

Describe dynamic equilibrium in a closed system as the state in which the forward and reverse reactions occur at equal rates so that the concentrations of reactants and products remain constant

Write the equilibrium constant expression Kc for a homogeneous reaction from its balanced equation, and interpret the magnitude of Kc as a measure of the extent of reaction

Apply Le Chatelier's principle to predict and explain the effect of a change in concentration, pressure or temperature on the position of equilibrium and on the yield of product, and explain why a catalyst changes neither the position of equilibrium nor the value of Kc

Explain why only a change in temperature changes the value of Kc, and predict the direction of that change from the sign of the enthalpy change of the forward reaction

(HL) Calculate Kc from equilibrium concentrations, and determine equilibrium concentrations from initial amounts and Kc using an initial–change–equilibrium table, including cases where the approximation that x is small is justified

(HL) Calculate the reaction quotient Q from concentrations that are not at equilibrium, and compare Q with Kc to predict the direction in which the reaction proceeds