Graham’s law

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Graham’s law, named after the Scottish chemist Thomas Graham, describes the relationship between the rates of diffusion or effusion of two gases and their molar masses. The law states that the rate of diffusion or effusion of a gas is inversely proportional to the square root of its molar mass. For example, consider the diffusion of helium (with a molar mass of about 4 g/mol) and sulfur hexafluoride (with a molar mass of about 146 g/mol). According to Graham’s law, helium, being lighter, will diffuse much faster than sulfur hexafluoride under the same conditions. This principle emphasizes the core idea that lighter gases diffuse or effuse more rapidly than heavier gases.

Graham’s law is mathematically expressed as:

$$\frac{R_{1}}{R_{2}} = \sqrt{\frac{M_{2}}{M_{1}}}$$

where R₁ and R₂ represent the rates of diffusion or effusion of two different gases, and M₁ and M₂ represent their respective molar masses. This equation demonstrates that the rate at which a gas diffuses or effuses is inversely proportional to the square root of its molar mass.

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Related

• Gas laws

More topics

• Boyle’s law
• Charles’s law
• Gay-Lussac’s law
• Avogadro’s law
• Ideal gas law
• Dalton’s law
• Henry’s law
• Combined gas law
• Graham’s law

External links

• Graham’s law – Wikipedia
• 2.9: Graham’s Laws of Diffusion and Effusion – Chemistry LibreTexts
• Graham’s Law of Diffusion vs. Effusion | Formula & Differences – Study.com
• Thomas Graham – Purdue University
• Gas Law – Graham’s Law of Effusion: Ten Examples – ChemTeam
• Graham’s Law: Definition, Examples & Equation – StudySmarter UK
• Graham’s law of diffusion | physics – Britannica
• Graham’s Law — Overview & Calculation – Expii
• Graham’s Formula for Diffusion and Effusion – ThoughtCo
• Graham’s Law of Effusion – ChemTalk
• What Is Graham’s Law in Chemistry? – ThoughtCo
• Graham’s Law – AK Lectures