How this calculator works
Compare gases at the same temperature under comparable conditions. Lighter molecules effuse faster through a small opening into low pressure. Graham scaling can serve as an idealized diffusion comparison, but real diffusion in a mixture depends on collisions and composition. Equal-amount traversal times have the inverse ratio of rates.
Formula
r1/r2 = sqrt(M2/M1); t1/t2 = sqrt(M1/M2).
Worked example
Gases with molar masses 4 and 16 g/mol have rate ratio 2 and equal-amount time ratio 0.5. Molar masses 4 and 36 g/mol give rate ratio 3.
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Frequently asked questions
Which gas belongs in the numerator?
The rate numerator is gas 1; the mass numerator inside the square root is gas 2.
Can I use different rate units?
Convert rates to the same unit before entering them.
Does this predict a diffusion coefficient?
No. Use a transport model for quantitative diffusion coefficients.