Which statement best explains why different gases effuse at different rates?

• A. Gases with higher molar mass effuse faster because they have more energy.
• B. Gases with lower molar mass effuse faster because their molecules move more quickly.
• C. Effusion rate depends only on the temperature and not on the type of gas.
• D. All gases effuse at the same rate regardless of their molar mass.

Answer: (B)

Verified step by step guidance

1. Understand the concept of effusion: Effusion is the process by which gas particles pass through a tiny opening without collisions between particles.
2. Recall Graham's Law of Effusion, which states that the rate of effusion of a gas is inversely proportional to the square root of its molar mass. Mathematically, this is expressed as \(\text{Rate} \propto \frac{1}{\sqrt{M}}\), where \(M\) is the molar mass of the gas.
3. Recognize that at the same temperature, lighter gas molecules (with lower molar mass) move faster on average than heavier molecules, because kinetic energy is related to temperature and velocity by \(KE = \frac{1}{2}mv^2\) and all gases have the same average kinetic energy at a given temperature.
4. Conclude that gases with lower molar mass effuse faster because their molecules have higher average speeds, allowing them to pass through the opening more quickly.
5. Therefore, the correct explanation is that gases with lower molar mass effuse faster due to their higher molecular speeds, not because of having more energy or temperature differences.