Explore AP Chemistry 3.5.A questions on relating particle motion and kinetic energy to the macroscopic properties of gases.
A student investigates gas behavior using a rigid cylinder with a movable piston of negligible mass, as shown in the diagram above. The cylinder contains 0.325 mol of O2(g).
The student tries to change the density of the O2(g) by cooling the cylinder to -55°C, which causes the volume of the gas to decrease. Using principles of kinetic molecular theory, explain why the volume of the O2(g) decreases when the temperature decreases to -55°C.
For a valid explanation: 1 point
Accept one of the following:
- As the gas cools, the average kinetic energy (speed) of the O2 molecules decreases. The molecules rebound with less energy when they collide with each other and the walls of the container. The spacing between particles decreases, causing the volume occupied by the gas to decrease.
- As the gas cools, the average kinetic energy (speed) of the O2 molecules decreases. The molecules rebound with less energy when they collide with each other and the walls of the container. The only way for the molecules to maintain a constant rate of collisions with the walls of the container (maintaining a pressure of 1.00 atm) is for the volume of the gas to decrease.