Which phase change increases entropy?

Which phase change increases entropy?

• A. Sublimation of a solid to a gas
• B. Freezing of a liquid
• C. Condensation of a gas
• D. Deposition of a gas to a solid

Answer: (C)

Entropy measures how disordered the system is. A phase change that increases disorder raises entropy. Going from a solid directly to a gas—sublimation—frees molecules from a rigid lattice and gives them full translational motion in all directions, vastly increasing the number of possible microstates. In contrast, freezing (liquid to solid), condensation (gas to liquid), and deposition (gas to solid) all reduce disorder by making the molecules more orderly or confined. Thus, the phase change that increases entropy is the solid-to-gas transition, sublimation.

Entropy measures how disordered the system is. A phase change that increases disorder raises entropy. Going from a solid directly to a gas—sublimation—frees molecules from a rigid lattice and gives them full translational motion in all directions, vastly increasing the number of possible microstates. In contrast, freezing (liquid to solid), condensation (gas to liquid), and deposition (gas to solid) all reduce disorder by making the molecules more orderly or confined. Thus, the phase change that increases entropy is the solid-to-gas transition, sublimation.