Latent Heat & Phase Change — A/L Physics

Latent Heat The thermal energy absorbed or released by a substance during a phase change at constant temperature. During melting, boiling, or sublimation, energy is used to overcome intermolecular forces (breaking bonds) rather than raising kinetic energy (temperature). Conversely, during freezing, condensation, or deposition, energy is released as bonds form. For example, ice at 0°C absorbs latent heat to become water at 0°C without temperature change.

Specific Latent Heat of Fusion (Lf) The energy required to change 1 kg of a substance from solid to liquid (or vice versa) at its melting point, without temperature change. For water, Lf = 3.34 × 10⁵ J kg⁻¹. This is why ice cubes in a drink absorb heat from the liquid to melt, cooling the drink without warming the ice above 0°C until fully melted.