The measure of the average kinetic energy of a substance is defined as which property?

• A. Temperature
• B. Pressure
• C. Volume
• D. Density

Answer: (A)

Temperature reflects the average kinetic energy of the particles in a substance. In the motion of molecules, how fast they move on average determines how much energy they carry as kinetic energy. When temperature rises, the average speed increases, so the particles have more kinetic energy; when temperature falls, their speeds and energies drop. This direct link is why temperature is used as a measure of average kinetic energy. Pressure and volume describe other aspects of matter—the force of particle collisions with container walls and the space available for motion, respectively—while density relates to how much mass is packed into a given volume, not the energy of particle motion. In an ideal gas, the average kinetic energy is proportional to temperature, reinforcing why temperature is the best descriptor of average kinetic energy.