Molecular systems tend to move spontaneously to a state of maximum randomness or disorder. molecular randomness, or disorder, is called entropy and is denoted by the symbol s. as a state function, entropy change, ? s, depends only on initial and final states. ? s has a positive value when disorder increases and a negative value when disorder decreases. the following conditions usually result in an increase in entropy:

a change of phase: solid? liquid? gas,

an increase in the number of gas molecules, or

a solid dissolving to form a solution.

although the sign of the entropy change can be predicted as described above, the actual value of ? s? must be calculated from the absolute entropy values, s? , of the reactants and products:

? s? =s? (products)? s? (reactants)