EQUILIBRIUM AND THE LAW OF MASS ACTIONThe law of mass action states: at equilibrium, the composition of a reaction mixture can be expressed in terms of the equilibrium constant. The equilibrium constant, K, is equal to the activities of the products raised to the power of their coefficients in the balanced chemical equation divided by the activities of the reactants raised to the power of their coefficients.-For pure solids or liquids the activity = 1 (no units).-For components of an ideal solution, the activity of each component is the ratio of its molar concentration to a reference standard concentration of 1M (therefore, units cancel). -For a mixture of gases, the activity of each component is the ratio ofits partial pressure to a reference standard pressure of 1 atm (therefore, units cancel).-For reactions mixtures that involve ions in solution, we write the equilibrium constant for the net ionic equation using activities of ions. Heterogeneous equilibria involve species in more than one phase. While homogeneous equilibria involve all species in the same phase.For mixtures of gases, K can be referred to as Kp. (Partial pressures are always in atmosphere for the calculation of Kp)THE EXTENT OF REACTIONThe equilibrium constant, K, indicates the extent to which a reaction can occur. A large equilibrium constant tells us that most of the reactants are converted into products before equilibrium is established. On the other hand, a small equilibrium constant indicates that only small amounts of reactants were converted into products.The value of Kis constant at constant temperature and changes if the temperature changes.The value of K does not depend on the initial concentrations.