# High School Chemistry : Help with Melting and Freezing

## Example Questions

### Example Question #1 : Phase Diagrams And Transitions

During the process of freezing, what do you know about changes in the temperature and entropy of water?

The temperature remains constant and the entropy increases

The temperature remains constant and the entropy decreases

The temperature decreases and the entropy decreases

The temperature remains constant and the entropy remains constant

The temperature increases and the entropy decreases

The temperature remains constant and the entropy decreases

Explanation:

The temperature of a sample during the process of a phase change will remain constant. Even though heat may be added or removed during this process, it is utilized to directly impact the formation and breaking of intermolecular interactions within the sample. The result is a change in the internal properties of the sample (the phase), with no actual change in temperature.

When a substance freezes it transitions from a liquid to a solid. The result is a much more ordered structure, as opposed to the fluidity associated with the liquid phase. Increasing order corresponds to a decrease in entropy because entropy is a measure of disorder.

### Example Question #1 : Phase Diagrams And Transitions

Which of the following is associated with freezing, for most substances?

Particles move more quickly and are farther apart from each other

Particles move more slowly and are further apart from each other

Particles move more quickly and are closer together to each other

Particles move more slowly and are closer to each other

Particles move more slowly and are closer to each other

Explanation:

When a substance freezes, the average kinetic energy of the particles decreases. This means that the particles will move more slowly. Most substances also contract when they cool to increase the organization of the molecules (crystallization). Thus, for most substances, particles will get closer together as they freeze. One notable exception is water, which expands as it freezes (the same mass of water that freezes into ice will float in liquid water due to an increase in volume).

### Example Question #1 : Phase Diagrams And Transitions

The following is the phase diagram for .

What state change is occurring on from point A to point G?

Sublimation

Melting

Condensation

Vaporization

Freezing