What this calculator does
Graham's law of effusion/diffusion works out relative rate at which two gases effuse or diffuse, from their molar masses. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
Formularate₁/rate₂ = √(M₂/M₁)
The inputs explained
| Field | What to enter |
|---|---|
| Molar mass of gas 1 (M₁) (g/mol) | A number, measured in g/mol. Starts at 2.016. |
| Molar mass of gas 2 (M₂) (g/mol) | A number, measured in g/mol. Starts at 32. |
| Known rate of gas 1 (units) | A number, measured in units. Starts at 4. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with molar mass of gas 1 (m₁)
Every other input is held at the calculator’s starting values while molar mass of gas 1 (m₁) varies. Select any row to load that scenario into the calculator.
How the answer changes with molar mass of gas 1 (m₁)
| Molar mass of gas 1 (M₁) (g/mol) | Rate₁ / Rate₂ | Rate of gas 2 | Lighter gas |
|---|---|---|---|
| 1.01 | 5.629 | 0.711 units | gas 1 (effuses faster) |
| 1.51 | 4.603 | 0.869 units | gas 1 (effuses faster) |
| 2.02 | 3.980 | 1.005 units | gas 1 (effuses faster) |
| 3.02 | 3.255 | 1.229 units | gas 1 (effuses faster) |
| 4.03 | 2.818 | 1.420 units | gas 1 (effuses faster) |
| 6.05 | 2.300 | 1.739 units | gas 1 (effuses faster) |