Q. What is Spontaneous reactions?

Ans.

Spontaneous reactions can occur under specific conditions without any assistance. Most of the reactions you know are spontaneous reactions. Under the right sort of conditions they will proceed on their own. Burning a candle is a spontaneous reaction; one the candle has been lit is proceeds without help.

It may seem that all spontaneous reactions are exothermic processes; that the release of energy is the determining factor in whether the reaction will occur. It turns out that this is an incorrect assumption. The spontaneity of a reaction is determined by more than the energy change of the reaction. When you place a drop of food coloring in water the color will disperse evenly throughout the water without stirring or temperature change. Try it and see!

In fact there are endothermic processes which are spontaneous. When you hang clothes out to dry, the conversion from liquid water to water vapor requires energy. Yet, evaporation occurs spontaneously.