Reviewed CSCA Chemistry question · Easy

A pure substance is slowly cooled from 150°C to -20°C at 1 atm. During cooling, it changes from gas to liquid at 80°C and then from liquid to solid at -10°C. Which of the following statements correctly describes the changes of state?

The gas-to-liquid change is called freezing and the liquid-to-solid change is called condensation.
The gas-to-liquid change is called condensation and the liquid-to-solid change is called freezing.
The gas-to-liquid change is called sublimation and the liquid-to-solid change is called deposition.
The gas-to-liquid change is called evaporation and the liquid-to-solid change is called melting.

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Correct answer

B. The gas-to-liquid change is called condensation and the liquid-to-solid change is called freezing.

Principle or equation

Changes of state: gas to liquid is condensation; liquid to solid is freezing. Opposite of vaporization and melting respectively.

Why this answer is correct

When a gas is cooled, it condenses to a liquid. Further cooling causes the liquid to freeze into a solid. Thus the first change is condensation, the second is freezing.

Example

Steam condenses to water at 100°C; water freezes to ice at 0°C.

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