KEY2CHEM

Gas Law Relationships

Changes in the macroscopic properties of a gas result from changes on the atomic or molecular level. For example, at constant pressure, the volume of a gas increases as the temperature increases. This is because the average kinetic energy of the particles increases as temperature increases, resulting in more frequent collisions with the walls of the container, which leads to an increase in volume. In order to make a direct relationship between two variables, the remaining properties must be held constant.

Example 1.

At constant temperature, as volume decreases, pressure ______.

A. increases

B. decreases

C. does not change

Solution

A. increases

As gas particles are confined to a smaller volume, the particles collide with one another and the container walls. Since $$\text{pressure} = \frac{\text{force}}{\text{area}}$$ and the area where the particles are colliding is smaller, the pressure is greater.

Example 2.

At constant volume, as temperature increases, pressure _____.

A. increases

B. decreases

C. does not change

Solution

A. increases

Increased temperature yields increased average kinetic energy. The particles collide with the container walls with greater force and with increased frequency, resulting in higher pressure.

Example 3.

At constant pressure and temperature, as gas amount increases, volume _____.

A. increases

B. decreases

C. does not change

Solution

A. increases

An increase in number of particles results in an increase in frequency of collisions, resulting in greater volume.