Equilibrium Constants

The equilibrium constant (Kc) is a value that expresses the ratio of the concentrations of the products to the reactants at equilibrium, each raised to the power of their stoichiometric coefficient.
For a generic reaction aA + bB ⇌ cC + dD, the equilibrium constant expression is given by Kc = ([C]^c[D]^d)/([A]^a[B]^b).

Factors Affecting Equilibrium Constants

Temperature: Equilibrium constants can be affected by temperature. An increase in temperature shifts the equilibrium for an endothermic reaction to the right, increasing Kc. A decrease in temperature shifts the equilibrium for an exothermic reaction to the right, increasing Kc.
Pressure and Concentration: Changes in pressure and concentration can shift the position of the equilibrium, but they do not affect the value of the equilibrium constant.

Applications of Equilibrium Constants

Predicting the Direction of Reactions: If the reaction quotient (Q) is greater than the equilibrium constant (Kc), the reaction will shift to the left, towards the reactants. If Q<Kc, the reaction will shift to the right, towards the products.

Le Chatelier’s Principle

Le Chatelier’s principle helps to predict what effects changes in temperature, concentration or pressure will have on the position of the equilibrium in a reaction.

Haber Process

A key industrial application of equilibrium constants and Le Chatelier’s principle is the Haber process for the production of ammonia. In the process, nitrogen and hydrogen gases are combined at high temperatures and pressures to create ammonia. The conditions have to be carefully controlled in order to optimally balance rate of reaction and yield.

Note: It is essential to have a clear understanding of the equilibrium constants and how they are applied in the chemical industry, as this forms a major part of the assessment in this topic.