How does the molecular motion of a substance change when it transitions from the liquid phase to the solid phase?

• A. Molecular motion stops completely as particles are locked in place.
• B. Molecular motion increases as particles move more freely.
• C. Molecular motion decreases as particles become more fixed in position.
• D. Molecular motion remains unchanged during the phase transition.

Answer: (C)

Verified step by step guidance

1. Understand that molecular motion refers to the movement of particles such as atoms or molecules within a substance, which includes vibrations, rotations, and translations.
2. Recall that in the liquid phase, molecules have more freedom to move around compared to the solid phase, where they are more tightly packed.
3. Recognize that during the transition from liquid to solid (freezing or solidification), the molecules lose some of their kinetic energy and become more fixed in position, reducing their overall motion.
4. Note that molecular motion does not stop completely in the solid phase; molecules still vibrate in place but do not move freely as in liquids.
5. Conclude that the correct description is that molecular motion decreases as particles become more fixed in position when transitioning from liquid to solid.