Latent heat is energy transferred per unit mass during a phase change, without a temperature change during the transition.

What does latent heat of fusion describe?

The energy per unit mass needed for melting, or released during freezing. It is represented by $L_f$ and measured in joules per kilogram.

What does latent heat of vaporization describe?

The energy per unit mass needed to vaporize a liquid, or released during condensation. It is represented by $L_v$ and measured in joules per kilogram.

Why can temperature stay constant during melting?

The transferred energy helps overcome molecular attractions and change the phase, rather than increase the molecules' average kinetic energy.

What is the general latent-heat equation?

The magnitude of energy transferred is $Q=mL$, where $m$ is mass and $L$ is the latent heat for the phase transition.

General physicsLesson 2 of 2 in the course Heat and Heat Transfer Methods

Latent Heat, Heating Curves, and Multistage Phase Changes

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

This lesson explains why a substance can absorb or release heat without changing temperature during a phase change.

A phase change is a transition between solid, liquid, and gas. Melting changes a solid into a liquid; freezing changes a liquid into a solid; vaporization changes a liquid into a gas; and condensation changes a gas into a liquid.

When ice melts at its melting point, its temperature remains constant until the melting is complete. The energy transferred does not increase the molecules' average kinetic energy, which is associated with temperature. Instead, energy helps overcome the attractive forces holding molecules in their solid arrangement. Vaporization also requires energy to separate interacting molecules in a liquid.

All flashcards

What is latent heat?: Latent heat is energy transferred per unit mass during a phase change, without a temperature change during the transition.
What does latent heat of fusion describe?: The energy per unit mass needed for melting, or released during freezing. It is represented by $L_f$ and measured in joules per kilogram.
What does latent heat of vaporization describe?: The energy per unit mass needed to vaporize a liquid, or released during condensation. It is represented by $L_v$ and measured in joules per kilogram.
Why can temperature stay constant during melting?: The transferred energy helps overcome molecular attractions and change the phase, rather than increase the molecules' average kinetic energy.
What is the general latent-heat equation?: The magnitude of energy transferred is $Q=mL$ , where $m$ is mass and $L$ is the latent heat for the phase transition.

Quiz questions

How does evaporation differ from boiling?Answer: Evaporation can occur at the liquid's surface below its boiling point.
Why does high humidity make perspiration less effective at cooling the body?Answer: Water evaporates more slowly when the air already contains substantial water vapor.
What is sublimation?Answer: A direct transition from solid to gas without passing through the liquid phase.
In an insulated system, how are the energy transfers between its parts related?Answer: Energy gained by some parts equals energy lost by other parts.
What happens to energy when water vapor condenses?Answer: The condensing substance releases energy to its surroundings.

Based on College Physics 2e by Paul Peter Urone, Roger Hinrichs (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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