Absolute Entropy

When the temperature of a substance is increased, the translational, vibrational and rotational motions become more vigorous. It leads to greater disorder and as a result the entropy of the substance increases. Thus, on increasing the temperature of a substance the entropy of a substance increases. It decreases on decreasing the temperature of a substance.

According to Walther Nernst, the entropy of a pure perfectly crystalline substance approaches zero as the temperature approaches absolute zero. This is known as the Third law of thermodynamics. This third law of thermodynamics helps to calculate the absolute value of molar entropies (S_m) of substances at different temperatures.