Graham's Law Calculator

Graham's Law states that lighter gases diffuse and effuse faster than heavier ones — the Graham's Law Calculator compares the diffusion or effusion rates of any two gases based on their molecular weights. Enter the Molar Mass of Gas A and Molar Mass of Gas B (or use the quick-pick presets for common gases) to get the Rate Ratio (A/B), the calculated rate of Gas A, the mass ratio, and a speed factor showing how many times faster one gas moves relative to the other.

g/mol

Enter molar mass in grams per mole

g/mol

Enter molar mass in grams per mole

relative units

Leave blank to calculate, or enter known rate

relative units

Reference rate (default = 1)

Results

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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Frequently Asked Questions

What is Graham's law of diffusion?

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.

Will a gas with higher molecular weight diffuse faster?

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.

Can you use Graham's law of effusion on diffusion?

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.

Do I need temperature or pressure for Graham's law calculations?

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.

What units should I use for molar mass?

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.

How can you use Graham's law of diffusion in real applications?

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.

What's the difference between diffusion and effusion?

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.