How do you calculate the equilibrium constant (Kc)?

The equilibrium constant (Kc) is calculated by dividing the product of the concentrations of the products by the product of the concentrations of the reactants.

In a chemical reaction, the equilibrium constant (Kc) is a measure of the ratio of the concentrations of the products to the concentrations of the reactants at equilibrium. It is calculated using the law of mass action, which states that the rate of a chemical reaction is directly proportional to the product of the concentrations of the reactants.

To calculate Kc, you need to know the balanced chemical equation for the reaction and the concentrations of all reactants and products at equilibrium. The general formula for Kc is:

Kc = [C]^c [D]^d / [A]^a [B]^b

In this formula, [A], [B], [C], and [D] represent the molar concentrations of the reactants (A and B) and products (C and D) at equilibrium. The lowercase letters (a, b, c, d) represent the coefficients from the balanced chemical equation.

For example, consider the reaction: aA + bB ⇌ cC + dD. At equilibrium, if the concentrations of A, B, C, and D are [A], [B], [C], and [D] respectively, then the equilibrium constant expression is given by the formula above.

It's important to note that the concentrations are raised to the power of their stoichiometric coefficients in the balanced chemical equation. Also, pure solids and liquids do not appear in the equilibrium expression as their concentrations are considered to be constant.

Remember, the value of Kc does not have units. It is a ratio and provides information about the extent of a reaction at equilibrium. A large Kc value indicates that the reaction favours the products, while a small Kc value indicates that the reaction favours the reactants.