Phase Changes: Equilibrium, Phase Diagrams, and Latent Heat

All flashcards

What is a phase transition?

A phase transition is a change from one physical phase of a substance to another, such as melting from solid to liquid.

How do melting and freezing differ?

Melting changes a solid into a liquid; freezing changes a liquid into a solid. They are reverse processes.

What is the difference between evaporation and boiling?

Evaporation is vaporization that can occur at a liquid’s surface. Boiling is rapid vaporization throughout a liquid when its vapor pressure reaches the ambient pressure.

How does pressure usually affect boiling point?

Increasing pressure usually raises the boiling point, while decreasing pressure usually lowers it.

Why is water unusual when pressure affects melting?

Ice is less dense than liquid water. Increasing pressure favors the denser liquid and therefore lowers the melting point of ice.

Quiz questions

1. What does the critical point mark on a phase diagram?Answer: The endpoint of the liquid–gas phase boundary.
2. What occurs at a substance’s triple point?Answer: Solid, liquid, and gas coexist in stable equilibrium.
3. In a closed container at equilibrium, what happens to evaporation and condensation rates?Answer: They occur at equal rates, so the amounts of liquid and vapor remain steady.
4. How is the magnitude of energy transferred during a phase change calculated?Answer: Multiply the substance’s mass by the relevant latent heat.
5. In an insulated calorimetry system, how are the heat transfers of the warmer and cooler parts related?Answer: Their heat transfers sum to zero: heat lost balances heat gained.