How to Write the Equilibrium Constant Expression?
1. Write the balanced chemical equation for the equilibrium reaction. By convention, the substances on the left of the equation are called the reactants and those on the right, the products.
2. Write the product of concentrations of the ‘products’ and raise the concentrations of each substance to the power of its numerical quotient in the balanced equation.
3. Write the product of concentrations of ‘reactants’ and raise the concentration of each substance to the power of its numerical quotient in the balanced equation.
4. Write the equilibrium expression by placing the product concentrations in the numerator and reactant concentrations in the denominator. That is,
Give the equilibrium constant expression for the reaction N2 + 3H2 ⇌ 2NH3
The equation is already balanced. The numerical quotient of H2 is 3 and of NH3 is 2.
The concentration of the product NH3 is [NH3]2
The product of concnentrations of the reactants is [N2] [H2]3
Therefore, the equilibrium constant expression is
