International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

When the pressure of gas is increased, what is the primary effect on gas particles?

1. They have more volume

2. They move slower

3. They collide more frequently due to decreased space

4. They become inactive

The correct answer is: They collide more frequently due to decreased space

When the pressure of a gas is increased, the primary effect on the gas particles is that they collide more frequently due to decreased space. Pressure in a gas is defined as the force exerted by gas particles as they collide with the walls of their container. When the pressure increases, it typically means that the volume of the container is being decreased or that additional gas is being added without changing the volume. As the volume decreases, the distance between individual gas particles becomes smaller, leading to more frequent collisions among the particles and between the particles and the walls of the container. This frequent interaction is a fundamental principle of gas behavior, described by the kinetic molecular theory, which states that gas particles are in constant motion and will collide more often when they are constrained to a smaller volume. The other options do not accurately describe the primary response of gas particles to increasing pressure. For instance, increasing pressure does not result in the particles having more volume or moving slower—both of which would occur under different conditions. Similarly, while gas particles do not become inactive, they are constantly in motion and responding to changes in their environment. Thus, the correct understanding of gas behavior under increased pressure is highlighted through the frequency of collisions as the space available to the particles decreases.