Which gas will have the highest rate of effusion at the same temperature?

Which gas will have the highest rate of effusion at the same temperature?

• A. Hydrogen
• B. Oxygen
• C. Nitrogen
• D. Carbon Dioxide

Answer: (A)

Effusion rate at a given temperature follows Graham's law: rate is inversely proportional to the square root of the molar mass. Lighter molecules move faster on average, so they pass through a tiny hole more quickly. Hydrogen has the smallest molar mass (about 2 g/mol) among the options, so its molecules have the highest average speed and effuse the fastest. You can see this with quick comparisons: hydrogen would effuse about 3.7 times as fast as nitrogen (√28/2 ≈ 3.74), about 4 times as fast as oxygen (√32/2 = 4), and about 4.7 times as fast as carbon dioxide (√44/2 ≈ 4.69).

Effusion rate at a given temperature follows Graham's law: rate is inversely proportional to the square root of the molar mass. Lighter molecules move faster on average, so they pass through a tiny hole more quickly. Hydrogen has the smallest molar mass (about 2 g/mol) among the options, so its molecules have the highest average speed and effuse the fastest. You can see this with quick comparisons: hydrogen would effuse about 3.7 times as fast as nitrogen (√28/2 ≈ 3.74), about 4 times as fast as oxygen (√32/2 = 4), and about 4.7 times as fast as carbon dioxide (√44/2 ≈ 4.69).