What happens to the standard molar entropy of a substance as temperature decreases toward absolute zero?

The standard molar entropy of a substance, as the temperature approaches absolute zero, follows the third law of thermodynamics, which states that the entropy of a perfect crystalline substance approaches zero as its temperature approaches absolute zero. This principle is based on the idea that at absolute zero (0 K), a perfectly ordered crystal lattice will have no thermal motion and, therefore, no entropy.

As the temperature decreases, the molecular motions that contribute to the randomness and disorder (which are indicators of entropy) also decrease. As the substance continues to cool down toward absolute zero, the entropy approaches zero because there are fewer possible microstates available for the system in this perfectly ordered state.

This behavior is fundamental in thermodynamics and helps define the absolute scale of entropy. It explains why materials at very low temperatures tend to behave in a more organized and predictable manner.