Why does adding heat make particles move faster?

• A. It increases their mass.
• B. It decreases their volume.
• C. It increases their kinetic energy.
• D. It changes their chemical identity.

Answer: (C)

Adding heat transfers energy to the particles, and temperature reflects the average kinetic energy of those particles. When energy is added, their kinetic energy increases, so they move faster and collide more vigorously. The amount of matter (mass) stays essentially the same, so the speed-up isn’t about having more stuff, but about having more energy per particle. Volume changes can occur because of thermal expansion, but that doesn’t cause the particles to move faster—it’s a separate consequence of heating. The chemical identity of the particles doesn’t change just from heating (unless a chemical reaction occurs, which is a different process). The core reason faster motion happens is the rise in kinetic energy.