During a fire, a fuel's potential energy is converted to which form of energy?

• A. Dynamic energy
• B. Thermal energy
• C. Endothermic energy
• D. Kinetic energy

Answer: (D)

In combustion, the chemical potential energy stored in the fuel is released as the molecules rapidly move and collide, causing the surrounding air to heat up and gases to expand. That release mainly shows up as kinetic energy—the energy of motion—of the reacting molecules and the resulting hot gases. We experience this as heat, which is the thermal energy of the system, but at the fundamental level the energy becomes kinetic energy of particles increasing their motion. The other options don’t fit as the primary form: dynamic energy isn’t a standard category here, and endothermic describes a process that absorbs energy rather than a form of energy, while thermal energy is the result we perceive from the kinetic activity.