Equilibrium Constants (Kc and Kp)

The concept of equilibrium is crucial in understanding many chemical reactions. Equilibrium is the state in which the concentrations of the products and the reactants in a reaction do not change over time.
Equilibrium constants, Kc or Kp, are used to define the position of equilibrium.
Kc refers to the equilibrium constant in terms of concentration. It represents the ratio of the concentrations of products to the concentrations of reactants, each raised to the power of their stoichiometric coefficients in the balanced chemical equation.
To calculate Kc, take the product of the concentrations of the products, each raised to the power of their stoichiometric coefficient, divided by the product of the concentrations of the reactants, each raised to the power of their stoichiometric coefficient.
Kp, on the other hand, denotes the equilibrium constant in terms of partial pressures. It is similar to Kc but is applied to gases.
To calculate Kp, take the product of the partial pressures of the products, each raised to the power of their stoichiometric coefficient, divided by the product of the partial pressures of the reactants, each raised to the power of their stoichiometric coefficient.
Remember, pure solids and pure liquids are left out of the equilibrium expressions for both Kc and Kp.
If Kc or Kp is greater than 1, the equilibrium position is towards the products side (right). If it’s less than 1, the equilibrium position is towards the reactants’ side (left).
The magnitude of Kc or Kp indicates the extent of a reaction at equilibrium. A high Kc or Kp means the reaction proceeds mostly to completion, while a low Kc or Kp suggests that very little product is produced.
Change in temperature will alter the value of the equilibrium constant. This is the only factor that can change Kc or Kp because it affects the forward and reverse reaction rates differently.
Changes in pressure or concentration will shift the equilibrium position, but they do not change the value of the equilibrium constant.
Remember to practise using the Kc and Kp expressions in problem solving. This will require a good understanding of moles and converting between moles and volume (concentration), or between moles and pressure (for gases).
Also, keep in mind that the calculated value of Kc or Kp should always have a positive value, as it represents ratio of products to reactants in positively progressing chemical reactions.