Rank each set of substances in order of increasing standard molar entropy (S°). Explain your reasoning. b. H₂O(s); H₂O(l); H₂O(g)

Key Concepts

Standard Molar Entropy

Standard molar entropy (S°) is a measure of the amount of disorder or randomness in a system at standard conditions (1 bar, 25°C). It quantifies the energy dispersal in a substance, with higher values indicating greater disorder. Entropy increases with temperature and the number of microstates available to a substance.

Phase Changes and Entropy

The phase of a substance significantly affects its entropy. Generally, gases have higher entropy than liquids, which in turn have higher entropy than solids due to the increased freedom of movement and arrangement of particles. As a substance transitions from solid to liquid to gas, its entropy increases due to the greater molecular motion and disorder.

Comparative Entropy of Water Phases

In the case of water, the standard molar entropies of its phases can be ranked based on their molecular arrangements. Ice (H2O(s)) has the lowest entropy due to its ordered crystalline structure, followed by liquid water (H2O(l)), which has more disorder, and finally water vapor (H2O(g)), which has the highest entropy due to the greatest molecular freedom and disorder in the gaseous state.