# MCAT Physical : States of Matter

## Example Questions

### Example Question #31 : Phase Changes

A brass disk with an outer diameter of  has a  diameter hole cut through its center. If the disk is initially at  and is then placed into a freezer at , what is the final area of the hole?

The linear expansion coefficient for brass is:

Explanation:

First, find the original area of the hole, in square meters:

We will also convert the temperatures to Kelvin.

The linear thermal expansion equation is:

Similarly, the thermal expansion of an area is given by the equation:

We are given the value of the constant, we know the original area, and we have the change in temperature. Using these values, we can solve for the change in area.

Find the final area of the hole by adding the change in area to the original area.

### Example Question #1 : States Of Matter

Which of the following describes a transition from gas to solid?

Fusion

Deposition

Crystallization

Vaporization

Sublimation

Deposition

Explanation:

There are six possible phase changes between the three phases of matter. Deposition describes the change from gas to solid, while sublimation describes the transition from solid to gas. Freezing (crystallization) is the transition from liquid to solid, while fusion (melting) is the transition from solid to liquid. Condensation is the transition from gas to liquid, while vaporization (boiling) is the transition from liquid to gas.

### Example Question #1 : States Of Matter

What conditions best favor the gaseous state?

Low temperature and low pressure

High temperature and low pressure

Low temperature and high pressure

High temperature and high pressure

High temperature and low pressure

Explanation:

Low pressure ensures that the molecules are not confined to a more organized state such as liquid or solid, while high temperature means higher kinetic energy, which means that the molecules have more energy to move away from one another and into the gaseous state. Low temperature would mean molecules have less energy to move away from one another, and high pressure will force molecules to be in a more organized state.

### Example Question #2 : States Of Matter

Raining is an example of what type of phase change?

Sublimation

Evaporation

Condensation

Deposition

Condensation

Explanation:

Raining occurs when water vapors become liquid water in the sky. Deposition is the phase change from gas to solid, sublimation is the phase change form solid to gas, and evaporation is the phase change from liquid to gas.

### Example Question #2 : States Of Matter

What is the phase change at the contact point between an ice hockey player's skate and the ice?

Evaporation

Melting

Condensation

Deposition

Melting

Explanation:

Melting occurs because the skates apply pressure to the ice. Due to the negative slope of solid-liquid equilibrium line for water, increased pressure results in a change from solid to liquid. None of the other answer choices do not have to do with the equilibrium between solid and liquid.

### Example Question #41 : Phase Changes

Which of the following describes the concept of sweating?

Sweating results in a decreased body temperature because evaporation is endothermic

Sweating results in increased body temperature because evaporation is endothermic

Sweating results in increased body temperature because evaporation is exothermic

Sweating results in decreased body temperature because evaporation is exothermic

Sweating results in a decreased body temperature because evaporation is endothermic

Explanation:

Sweating reduces skin temperature because the sweat that is secreted to the skin evaporates, which is an endothermic process. Thus, heat is absorbed from the body and skin to drive the evaporation of the sweat on the skin.