Entropy

The entropy is the measure of disorder or randomness in a system. The greater the disorder in a system, the greater is the entropy of the system.

For a given substance,

• The crystalline state is the most ordered state, hence its entropy is the lowest.
• The gaseous state is the most disordered state, hence its entropy is the maximum.
• The disorder in the liquid state is intermediate between the solid and the gaseous state.

When a system changes from one state to another, the change of entropy ΔS is given by

ΔS = q_rev/T

where q_rev is the heat supplied reversibly at temperature T