Which of the following best describes what happens when the thermal energy of a substance increases?

• A. The substance's mass increases.
• B. The number of particles in the substance decreases.
• C. The particles in the substance move faster.
• D. The chemical composition of the substance changes.

Answer: (C)

Verified step by step guidance

1. Understand that thermal energy is related to the kinetic energy of particles in a substance, which means it affects how particles move.
2. Recall that increasing thermal energy does not change the mass of the substance, as mass is conserved and independent of temperature.
3. Recognize that the number of particles in a substance remains constant unless a chemical reaction or phase change involving particle loss occurs, which is not implied here.
4. Know that increasing thermal energy causes particles to move faster because their kinetic energy increases, leading to more vigorous motion.
5. Understand that the chemical composition of a substance remains unchanged by simply increasing thermal energy; chemical changes require breaking and forming bonds, which is not indicated in this scenario.