• Graham’s law relates the molecular mass of a gas to its rate of diffusion or effusion.
  • Diffusion and effusion are related to the speed at which various gas molecules move.
  • Gases that have a lower molar mass effuse and diffuse at a faster rate than gases that have higher molar masses.
  • The relative rates of diffusion of ammonia to hydrogen chloride can be observed in a simple experiment.
  • A helium-filled balloon will stop floating and sink to the floor after a day or so.
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