What is the measure of the average kinetic energy of a substance's molecules?

• A. Temperature
• B. Heat
• C. Conduction
• D. Vaporization

Answer: (A)

Temperature is the measure of the average kinetic energy of the molecules in a substance. When molecules move more vigorously, their kinetic energy is higher, which shows up as a higher temperature. Temperature describes how energetic the particles are on average, not how much total energy the substance contains. Heat, by contrast, is the energy that flows between objects because of a temperature difference, not a measure of motion itself. Conduction is a mode of transferring that heat through materials, and vaporization is a phase change that requires energy input. So temperature best describes the average kinetic energy of the molecules.