Question

Explain spontaneous and non-spontaneous processes, giving two examples of each.

Answer 1

A spontaneous processes takes place on its own without the external influence. Once started, a spontaneous processes proceeds on its own, without the continuous external help. For spontaneous processes, the change in Gibbs free energy is negative ($\Delta G<0$).
Examples of spontaneous processes:
1) Heat flows from hotter body to a colder body.
2) A solid KCl spontaneously dissolves in water.
A non-spontaneous processes does not takes place on its own. It needs continuous external influence.
Once started, a non-spontaneous processes will stop, when the continuous external force is withdrawn.
For non-spontaneous processes, the change in Gibbs free energy is positive ($\Delta G>0$).
Examples of non-spontaneous processes:
1) Flow of heat from inside of refrigerator to the room. Room is at higher temperature than refrigerator.
2) Boiling of water.