Enter the Molar Mass of Gas A and Molar Mass of Gas B (or use the Quick Pick dropdowns to select common gases) into this Graham's Law Calculator to find the Rate Ratio (A/B) — plus the Speed Factor, Mass Ratio, and individual effusion rates if you plug in a known rate for either gas.
Rate Ratio (A/B)
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Rate of Gas A
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Mass Ratio (B/A)
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Speed Factor
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Graham's law states that the rate of effusion or diffusion of a gas is inversely proportional to the square root of its molar mass. Lighter gases diffuse faster than heavier gases at the same temperature and pressure.
No, gases with higher molecular weight diffuse slower. According to Graham's law, diffusion rate is inversely related to the square root of molar mass, so lighter gases always diffuse faster.
Yes, Graham's law applies to both effusion (gas escaping through small holes) and diffusion (gas mixing with another gas). The mathematical relationship is the same for both processes.
No, temperature and pressure are not needed when comparing rates of two gases. Graham's law gives the ratio of rates, and T and P cancel out when both gases are at the same conditions.
Use grams per mole (g/mol) for molar mass. Since Graham's law calculates ratios, the specific units don't matter as long as both gases use the same units consistently.
Graham's law is used in gas separation processes, uranium enrichment, gas leak detection, and understanding how different gases spread in the atmosphere. It's also important in respiratory physiology and industrial gas processing.
Diffusion is when gas molecules spread out and mix with other gases in open space. Effusion is when gas escapes through a small opening or pore. Graham's law applies to both processes with the same mathematical relationship.