Gibbs' Free Energy Change is given by #Delta#G =#Delta#H - T#Delta#S where #Delta#H is the change in Enthalpy associated with the reaction ,T is the temperature at which given reaction takes place and #Delta#S is the change in Entropy for the given reaction.
If the value of #Delta#G is negative,the reaction is said to be spontaneous ,if it is positive,the reaction is said to be non-spontaneous.
For the given reaction of conversion of liquid form water to solid form ice,the value of #Delta#S would be negative and thus -T#Delta#S would be positive.For the spontaneity of the reaction,the enthalpy change #Delta#H must be negative and its magnitude would be greater than magnitude of T#Delta#S.
