When a substance is heated, what typically happens to the kinetic energy of its molecules?

When a substance is heated, what typically happens to the kinetic energy of its molecules?

• A. They lose kinetic energy.
• B. They gain kinetic energy.
• C. Their kinetic energy stays the same.
• D. They disappear.

Answer: (B)

Heating adds energy to the substance, which raises the average kinetic energy of the molecules. Temperature is a measure of that average kinetic energy, so as you apply heat, the molecules move faster on average. In kinetic theory, the average translational kinetic energy is proportional to temperature, so more heat means higher kinetic energy and faster molecular motion. Note that during a phase change, the added heat can go into breaking intermolecular bonds, so the temperature (and thus the average kinetic energy) can stay constant until the phase change is complete; after that, heating again increases kinetic energy. So, the typical outcome is that the molecules gain kinetic energy.

Heating adds energy to the substance, which raises the average kinetic energy of the molecules. Temperature is a measure of that average kinetic energy, so as you apply heat, the molecules move faster on average. In kinetic theory, the average translational kinetic energy is proportional to temperature, so more heat means higher kinetic energy and faster molecular motion. Note that during a phase change, the added heat can go into breaking intermolecular bonds, so the temperature (and thus the average kinetic energy) can stay constant until the phase change is complete; after that, heating again increases kinetic energy. So, the typical outcome is that the molecules gain kinetic energy.