Latent Heat

In-depth explanation of Latent Heat

Latent heat is the energy absorbed or released during a phase change at constant temperature and pressure. It is called latent because the energy does not show up as a temperature change, but instead goes into breaking or forming intermolecular attractions. Melting and boiling absorb heat, while freezing and condensation release the same amount. The specific latent heat of fusion of water is 334 joules per gram, and the specific latent heat of vaporization is 2260 joules per gram. Latent heat explains why steam is so hazardous and why evaporation cools the skin.

Going deeper: Latent Heat

Key ideas: Compute heat for a phase change as q equals m times latent heat, or n times molar enthalpy. For a heating curve, sum the heating segments with m c delta T and the plateau segments with latent heat. Temperature stays constant during the change.

Common mistakes and connections: Typical mistakes include applying m c delta T across a phase change and forgetting the plateaus. Fusion and vaporization values differ greatly because vaporization separates molecules completely. This idea links to enthalpy of phase change, entropy of phase change and refrigeration.

Visualization of Latent Heat

Temperature plateaus during melting and boiling because heat goes into breaking intermolecular attractions rather than raising kinetic energy. The interactive lesson shows this as a live animation or chart.

Worked example and use case

Steam burns are often more severe than boiling water burns, because condensing steam releases its latent heat of 2260 joules per gram onto the skin.

Where Latent Heat fits in Thermodynamics & Energetics

Latent Heat is topic 59 of 91 in Thermodynamics & Energetics.

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