Final answer:
The phase change from solid to liquid, such as ice melting into water, results in an increase in entropy due to the greater molecular disorder and larger number of microstates in the liquid phase.
Step-by-step explanation:
The phase change that results in an increase in entropy is the transition from a solid to a liquid or gas, or from a liquid to a gas. In particular, when water transitions from ice (solid) to water (liquid), there is an increase in entropy. This is because in the solid phase, water molecules are in a more ordered state with fewer microstates available, whereas in the liquid phase, the increased freedom of motion for the water molecules leads to a greater variation in possible particle locations, and thus a larger number of microstates. According to thermodynamics, the sign of the entropy change (ΔS) for melting is positive (ΔS > 0).
When considering the entropy as a measure of disorder, the melted ice (liquid water) represents a state with higher entropy than the ice (solid) due to the increase in molecular disorder and energy dispersal among the water molecules. Conversely, when water freezes (liquid to solid), entropy decreases because the molecules become more ordered. Hence, the corresponding sign of the entropy change would be negative (ΔS < 0).