What is latent heat?

What is latent heat?

• A. Energy required to change the state of 1 kg of a substance without changing its temperature.
• B. Energy required to raise the temperature of 1 kg by 1°C.
• C. Energy required to change the volume of a substance.
• D. Energy released when a substance changes state.

Answer: (A)

Latent heat is the energy involved in a phase change of a substance at a constant temperature. When a solid becomes a liquid or a liquid becomes a gas (or the reverse), the temperature doesn’t rise or fall during the change; instead, energy goes into rearranging the molecules to form a new phase. For a mass of 1 kg, the latent heat is the energy required to change that mass’s state at the transition temperature. That’s why the correct statement is about energy needed to change the state of 1 kg without changing its temperature. The other ideas describe different concepts: heat needed to raise temperature (specific heat and sensible heat), energy to change volume (not the defining feature of latent heat), and energy released during a phase change (which happens in some directions but not always).

Latent heat is the energy involved in a phase change of a substance at a constant temperature. When a solid becomes a liquid or a liquid becomes a gas (or the reverse), the temperature doesn’t rise or fall during the change; instead, energy goes into rearranging the molecules to form a new phase. For a mass of 1 kg, the latent heat is the energy required to change that mass’s state at the transition temperature.

That’s why the correct statement is about energy needed to change the state of 1 kg without changing its temperature. The other ideas describe different concepts: heat needed to raise temperature (specific heat and sensible heat), energy to change volume (not the defining feature of latent heat), and energy released during a phase change (which happens in some directions but not always).