Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

What causes gas pressure in a container?

1. Gravity acting on the gas molecules

2. Molecules striking the walls of the container

3. Temperature fluctuations

4. The chemical composition of the gas

The correct answer is: Molecules striking the walls of the container

Gas pressure in a container is primarily caused by molecules striking the walls of that container. When gas molecules move, they occupy space and collide with the surfaces surrounding them. Each collision exerts a force on the walls; the cumulative effect of all these collisions results in gas pressure. The kinetic theory of gases elaborates on this by stating that gas consists of a large number of molecules in constant, random motion. As these molecules collide with the walls, they transfer momentum, creating pressure. The more frequently and forcefully these collisions occur, the higher the pressure will be. While gravity does influence gas behavior, particularly in terms of buoyancy and the distribution of gas in a gravitational field, it does not directly create gas pressure in a closed system like a container. Temperature fluctuations and the chemical composition of the gas can affect the frequency and energy of molecular collisions but are not the primary causes of pressure itself. It is the actual impact of the moving molecules with the container's walls that directly generates gas pressure.