Equilibrium Constant: Applications
Equilibrium constant is useful in: Predicting the extent of a reaction Predicting the direction of a reaction Calculating equilibrium concentrations The magnitude of equilibrium constant provides a useful indication of the extent of a chemical reaction. The equilibrium constant for a reversible reaction is equal to the ratio of concentrations of product and the concentrations of the reactants.            A + B ⇌ C + D                Kc or Kp = $\frac{\text{[products]}}{\text{[reactants]}}$ The magnitude of equilibrium constant Kc and Kp indicates the extent to which a reaction will proceed. If the value of Kp>103, then the reaction proceeds to completion. If the value of Kp <10-3 then the reaction proceeds rarely. If the value of Kpis between10-3 to 103, then appreciable quantities of the reactants as well as the products are present. At any point in a reversible reaction, the ratio of the concentration of the products to that of the reactants is known as the reaction quotient Q (Qc with molar concentrations and Qp with partial pressures). Qc = $\frac{\text{[products]}}{\text{[reactants]}}$ Qc =   $\frac{{\text{[C]}}^{\text{c}}\text{}{\left[\text{D}\right]}^{\text{d}}}{{\text{[A]}}^{\text{a}}\text{}{\text{[B]}}^{\text{b}}}\text{}$ The reaction quotient expression of a reaction has the same equation as the equilibrium constant expression for that reaction. Reaction quotient is calculated using the concentrations or pressure at a given point of time in the reaction, and not its equilibrium concentrations or pressures. If Qc > Kc, backward reaction takes place. If Qc < Kc, forward reaction takes place. If Qc = Kc, the reaction is already at equilibrium.

#### Summary

Equilibrium constant is useful in: Predicting the extent of a reaction Predicting the direction of a reaction Calculating equilibrium concentrations The magnitude of equilibrium constant provides a useful indication of the extent of a chemical reaction. The equilibrium constant for a reversible reaction is equal to the ratio of concentrations of product and the concentrations of the reactants.            A + B ⇌ C + D                Kc or Kp = $\frac{\text{[products]}}{\text{[reactants]}}$ The magnitude of equilibrium constant Kc and Kp indicates the extent to which a reaction will proceed. If the value of Kp>103, then the reaction proceeds to completion. If the value of Kp <10-3 then the reaction proceeds rarely. If the value of Kpis between10-3 to 103, then appreciable quantities of the reactants as well as the products are present. At any point in a reversible reaction, the ratio of the concentration of the products to that of the reactants is known as the reaction quotient Q (Qc with molar concentrations and Qp with partial pressures). Qc = $\frac{\text{[products]}}{\text{[reactants]}}$ Qc =   $\frac{{\text{[C]}}^{\text{c}}\text{}{\left[\text{D}\right]}^{\text{d}}}{{\text{[A]}}^{\text{a}}\text{}{\text{[B]}}^{\text{b}}}\text{}$ The reaction quotient expression of a reaction has the same equation as the equilibrium constant expression for that reaction. Reaction quotient is calculated using the concentrations or pressure at a given point of time in the reaction, and not its equilibrium concentrations or pressures. If Qc > Kc, backward reaction takes place. If Qc < Kc, forward reaction takes place. If Qc = Kc, the reaction is already at equilibrium.

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