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Why can a substance absorb heat without becoming hotter?

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heating In a thermoelectric generating system a heat source—usually fueled by coal, oil, or gas—is used within a boiler to convert water to high-pressure steam. The steam expands and turns the blades of a turbine, which turns the armature of a generator, producing electric power. A condenser converts any remaining steam to water, and a pump returns the water to the boiler.

A substance can absorb heat without an increase in temperature when it undergoes a change in its physical state, such as melting, boiling, or sublimation. During these phase transitions, the absorbed energy—known as latent heat—is used to overcome the attractive forces holding the substance's atoms or molecules together, rather than increasing their kinetic energy, which would otherwise result in a rise in temperature.12

For example, when water boils at 100 °C, the temperature remains constant until the liquid has completely transitioned into vapor because all incoming heat is consumed as the latent heat of vaporization. Similarly, when ice melts at 0 °C, the added energy is used as the latent heat of fusion to break the crystal lattice structure, keeping the temperature stable until the transition to liquid is complete. This distinction between energy used for phase changes and energy used to raise temperature is essential for understanding sensible heat versus latent heat.12