What is the heat energy that causes a change in state and cannot be measured with a thermometer?

• A. Latent heat (Hidden heat)
• B. Specific Heat
• C. Sensible Heat
• D. Thermal Energy

Answer: (A)

Latent heat is the energy associated with a phase change that does not change the temperature. When a substance melts, freezes, boils, or condenses, energy goes into breaking or forming intermolecular bonds rather than increasing molecular motion. Because the temperature stays constant during these transitions (0°C for melting at standard pressure, 100°C for boiling), a thermometer can’t detect the heat being absorbed or released. That energy is latent heat, measured per unit mass for the specific phase change (fusion or vaporization).

Sensible heat, by contrast, is the heat that changes temperature and is what a thermometer reads. Specific heat describes how much energy is needed to raise the temperature by one degree per unit mass, and thermal energy is the total energy content. But the heat involved in changing state specifically—and not detectable as a temperature change—maps to latent heat.