Absolute Entropy

ABSOLUTE ENTROPY

The entropy of a pure crystalline substance at absolute zero temperature is zero. This is the statement of third law of thermodynamics.

This law provides an absolute reference point for the entropy called absolute entropy. It is very much useful in thermodynamic analysis of chemical reactions.

Entropy is simply defined as the amount by which the entropy of system changes from initial state to final state. But it is not measured in terms of absolute entropy. To determine the absolute entropy, a zero value of entropy of the system is arbitrarily chosen as a standard state. Then, the entropy change is calculated with respect to this standard state. For example, consider a system being at state 1,

Absolute entropy, ΔS = S1 - So

where

S1 = Entropy of system at state 1.

So = Entropy of system at standard state denoted 'o'.