Question

students designed an experiment to test how the movement of molecules in a substance changes. they measured the speed of the substance’s molecules and caused a phase change. how does the movement of the substance’s molecules change during a phase change? a. the molecules slow down as the substance changes into a gas. b. the molecules stop as the substance changes into a liquid. c. the molecules speed up as the substance changes into a solid. d. as the substance changes from a solid to a liquid, the molecules move faster.

Explanation:

To solve this, we analyze each option based on phase change concepts:

• Option A: A gas changing to a liquid is condensation. In condensation, gas molecules slow down (lose energy) and come closer, forming a liquid. This matches the description of molecules slowing and a phase change to liquid.
• Option B: A liquid to solid is freezing (molecules slow, but change to solid, not liquid). Eliminate.
• Option C: Solid to liquid is melting (molecules speed up, gain energy). Eliminate.
• Option D: Liquid to gas is evaporation/boiling (molecules speed up, gain energy). Eliminate.

Answer:

A. The substance’s molecules slowed down and the substance changed into a liquid.