What type of heat cannot be sensed directly?

Latent heat refers to the amount of heat required for a phase change of a substance, such as the transition from solid to liquid (melting) or liquid to gas (vaporization), without a change in temperature. During these processes, energy is absorbed or released by the substance, but this energy does not manifest as a sensed temperature change. Instead, it is 'hidden' within the phase change mechanisms, which is why latent heat cannot be sensed directly by temperature measuring devices like thermometers.

For example, when ice melts to become water, the temperature of the mixture remains at 0°C until all the ice has melted; only thereafter does the temperature begin to rise with further heat addition. Therefore, while the energy is indeed there, it does not manifest itself in a temperature change until the phase transition is complete. This unique characteristic of latent heat is what distinguishes it from other types of heat, which can be sensed directly.