An irreversible process always tends to take the isolated system to a state of greater disorder. An isolated system always tends to a state of greater entropy. So there is link between entropy and disorder. It may be roughly said that the entropy of a system is a measure of degree of molecular disorder existing in the system. When the heat is imparted to a system, the disorderly motion of the molecules increases and so the entropy of the system increases. The reverse occurs when the heat is removed from the system.
Summarizing the first and second law of thermodynamics, Clausius made two statements:
1) The energy of the world (universe) is constant.
2) The entropy of the world tends towards a maximum.
Thus the entropy of the isolated system tends to go on increasing and reaches maximum value at the state of equilibrium. When the system reaches equilibrium the increase in entropy becomes zero.