The formation of ice from water is exothermic in nature, but water does not convert into ice spontaneously at ordinary temperature and pressure, why?

Explanation

At a given temperature and pressure, a process will be spontaneous if it occurs with decrease in free energy. Again, at a fixed temperature and pressure. The free energy change of a system in a process is, `DeltaG=DeltaH-TDeltaS`, where `DeltaH and DeltaS` are enthalpy and enthalpy change of the system respectively.
During the conversion of water into ice, the entropy of the system decreases because the entropy of a liquid is greater than that of a solid. so, for the conversion of water into ice, `Delta S` is -ve. again, `DeltaH` is also -ve as it is an exothermic process. thus, both `DeltaH and TDeltaS` are -ve. but at ordinary temperature and pressure, `|TDeltaS|` is greater than `|DeltaH|`. hence, the value of `DeltaG` becomes +ve. so, the conversion of water into ice at ordinary temperature and pressure is not spontaneous.