Since, entropy is the measure of degree of randomness. So, more randomly the molecules of a substance are moving more will be its entropy.
For example, when a solid melts then it means heat is absorbed by it due to which its molecules have gained energy. As a result, they collide with each other and hence, entropy will increase.
Evaporation of a liquid will also cause the liquid to change its state from liquid to gas. This means molecules will go far away from each other leading to an increase in the entropy.
Sublimation is a process of conversion of a solid into gaseous phase without going through liquid phase. So, in this case also entropy will increase due to gain in energy by the molecules of a solid.
In freezing, molecules of a substance come closer to each other and acquire less energy. Hence, entropy decreases.
Mixing is a process of combining two or more substances physically with each other. This leads to increase in entropy of a substance.
In separation molecules are separated from each other leading to a decrease in energy. Hence, entropy will also decrease.
Diffusion is a process in which molecules are able to rapidly move from one place to another. Hence, entropy increases when diffusion takes place.
Thus, we can conclude that melting of a solid, evaporation of a liquid, sublimation, mixing and diffusion involve an increase in the entropy of the system under consideration.
