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Graham’s Law

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Graham’s Law


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You will explore Graham’s law of effusion by comparing the rate of effusion of two gases with the square root of their molar masses.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • Describe how gaseous diffusion can be used to separate isotopes of uranium.
  • Explain Graham’s Law as an inverse relationship between rate of effusion of a gas and the square root of its molar mass.
  • Determine the relative effusion rates of gases by considering their molar masses.
  • Identify an unknown gas using Graham’s Law.

Everything You'll Have Covered

Graham's Law states that the rate of effusion of a gas is inversely proportional to the molar mass of the gas. The lighter the gas, the faster it will effuse. Using Graham's Law, the identity of an unknown gas can be determined if it is compared to a known gas. The rate of gas 1 divided by the rate of gas 2 is equal to the square root of the molar mass of gas 2 divided by the square root of the molar mass of gas 1:

Tutorial Details

Approximate Time 20 Minutes
Pre-requisite Concepts Learners should know diffusion, isotopes, molar mass and rate.
Course Chemistry
Type of Tutorial Concept Development
Key Vocabulary chemistry, diffusion, effusion