Inputs
Choose a relation and the unknown variable. Provide the remaining values. All masses in g·mol⁻¹.Theory
Graham's law relates diffusion or effusion rates of two gases to the inverse square root of their molar masses.Rates: r₁ / r₂ = √(M₂ / M₁)
Times: t₁ / t₂ = √(M₁ / M₂)
Lower molar mass → faster diffusion/effusion; higher molar mass → slower.
- Applies at identical conditions of T, P, geometry.
- Use consistent units; the ratio cancels the units.
- For mixtures or non-ideal behavior, deviations can occur.
Tips
- Use the presets to quickly fill molar masses.
- Click Swap gases to swap M₁ and M₂.
- Adjust significant figures to match your data precision.
- Label rate or time units for clearer reporting.
FAQs
It predicts how the diffusion or effusion rates of two gases compare from their molar masses, assuming the same temperature, pressure, and apparatus.
Use the rate relation when you measure rate directly (e.g., cm·s⁻¹). Use the time relation when you measure how long a fixed distance or volume takes.
No, any consistent units work because they cancel in the ratio. Just keep the same unit for both gases.
Real gases and apparatus introduce friction, turbulence, or non-ideal effects. Temperature gradients and leaks can also cause deviations from the ideal relation.
Yes, molecular weight values in g·mol⁻¹ are numerically the same as molar mass values and can be used directly.
You choose. Gas A corresponds to r₁ or t₁ with molar mass M₁; Gas B corresponds to r₂ or t₂ with molar mass M₂. Swapping them inverts the ratio.
Match the significant figures to your measurements. The control lets you round the final value and the intermediate displays show the unrounded result.
Yes. Measure r or t for the unknown versus a reference of known molar mass and solve for the unknown using the appropriate relation.