Each system possesses a certain degree of order and a certain degree of randomness. The measure of the disorder of a system is called the entropy (S) of the system. The second law of thermodynamics states that reactions proceed such that entropy or chaos increases. Since entropy is a measure of disorder, it follows that the entropy of a solid is less than that of a liquid, which in turn is less than that of a gas. Likewise, free elements would appear to be less orderly than formed products. However, if the product is a solid and the reactants are gaseous, the reaction may move to favor the gaseous reactants with their higher entropy. The entropy is given mathematically by
In equation (1), k is the Boltzmann constant, equal in value to (the gas constant divided by Avogadro's number). The quantity W represents the disorder of the system. Its numerical value is given by the number of combinations under which the system maintains the same total energy. If the measurements are evaluated under standard conditions, the result is the standard entropy S¬°. The standard reaction entropy is
