Advanced Placement (AP) Chemistry Practice Exam

What is the definition of effusion in terms of gas behavior?

1. The rate at which a gas will escape through microscopic holes

2. The rate at which a gas expands to fill a container

3. The measure of how fast gas particles collide with the walls of a container

4. The process of gas mixing evenly with another gas

The correct answer is: The rate at which a gas will escape through microscopic holes

Effusion is specifically defined as the process by which gas particles escape from a container through tiny openings or microscopic holes. This definition emphasizes the behavior of gas molecules as they move from an area of higher pressure to one of lower pressure, allowing them to pass through these small openings. Notably, the rate of effusion can be influenced by factors such as the molecular weight of the gas, as described by Graham's law of effusion, which states that lighter gases effuse more rapidly than heavier gases. The other options refer to different behaviors of gases. The second option about gas expansion refers to diffusion, the process by which a gas fills the volume of a container uniformly. The third option describes gas pressure and is related to the kinetic molecular theory, which explains how gas particles collide with container walls. The fourth option relates to mixing, which occurs when different gases combine to form a uniform mixture, also categorized as diffusion. These distinct processes differ from effusion, which focuses solely on the escape of gas through small holes.