Equilibrium Constant

Name:
Equilibrium Constant
Detailed information:
A number that relates the concentrations of starting materials and products of a reversible chemical reaction to one another. For example, for a chemical reaction represented by the equation aAB + bCD ←→ cAD + dBC the equilibrium constant would be K = [(AD)^c(BD)^d]/[(AB)^a(CD)^b] where a, b, c, and d are the numbers of molecules of AB, CD, AD, and BC that occur in the balanced equation, and (AD), (BC), (AB), and (CD) are the molecular concentrations of AD, BC, AB, and CD in any mixture that is at equilibrium. At any one temperature, K is usually at least approximately constant, regardless of the relative quantities of the several substances, so that when K is known it is often possible to predict the concentrations of the products when those of the starting materials are known. The constant changes markedly with temperature. The constant can often be calculated from the relations of thermodynamics if the free energy for the chemical reaction is known, or by measuring all concentrations in one or more carefully conducted experiments.