Gas Laws and Assumptions

Multiple Choice

The pressure of a fixed mass of an ideal gas in a container is decreased at constant temperature. For the molecules of the gas there will be a decrease in:

• A

• B

• C

• D

​If the pressure of a fixed mass of an ideal gas in a container is decreased at constant temperature, the volume of the container must increase to maintain the same number of moles of gas.

As a result, the average distance between gas molecules increases, which decreases the frequency of collisions with the container walls.

This means that fewer gas molecules will strike the container walls every second, leading to a decrease in the pressure of the gas.

​The pressure of a fixed mass of an ideal gas in a container is decreased at constant temperature. For the molecules of the gas there will be a decrease in:

A. the mean square speed.
B. the number striking the container walls every second. 
C. the force between them. 
D. their diameter.

Multiple Choice

Under what conditions of pressure and temperature does a real gas approximate to an ideal gas?

• A

• B

• C

• D

At low pressures, the distance between gas molecules is large compared to their size, reducing intermolecular forces,

and at high temperatures, gas molecules have high kinetic energy, leading to greater distances between molecules.

Both factors lead to a decrease in the deviation from ideal gas behavior.

However, at high pressures and low temperatures, the volume of the gas molecules becomes significant, and intermolecular forces become more important, leading to deviations from ideal gas behavior.

​Under what conditions of pressure and temperature does a real gas approximate to an ideal gas?

Low Pressure

High Temperature

(Low density)

Multiple Choice

An ideal gas is in a closed container. Which changes to its volume and temperature when taken together must cause a decrease in the gas pressure?

• A

• B

• C

• D

An ideal gas is in a closed container because it does not interact with the container walls, meaning that the pressure it exerts is solely due to the motion of its particles.

A decrease in gas pressure can be caused by a decrease in the number of gas molecules striking the container walls per unit time.

This can occur if:

• the volume of the container increases, reducing the frequency of collisions with the walls, and if

• the temperature of the gas decreases, reducing the kinetic energy of the particles and the frequency of collisions.

​An ideal gas is in a closed container. Which changes to its volume and temperature when taken together must cause a decrease in the gas pressure?

Volume increases and Temperature decreases.