Gases assumed ideal
r ∝ 1/√M
Only molar mass or density matters for ratios. Keep T and P equal for both gases.
Density mode assumes same temperature and pressure for both gases.
g/mol
g/mol
Tip: 1 g/L equals 1 kg/m³ exactly; choose whichever unit you prefer.
s
Provide A or B time to compute the other (same distance).
s
cm
Provide A or B distance to compute the other (same time).
cm
Results
| Metric | Value | Definition |
|---|---|---|
| Rate ratio rA/rB | — | Relative effusion/diffusion rate |
| Time ratio tA/tB | — | Times to travel the same distance |
| Computed time A | — | When only one time is provided |
| Computed time B | — | When only one time is provided |
| Computed distance A | — | When only one distance is provided |
| Computed distance B | — | When only one distance is provided |
Formatting: results rounded to 6 significant figures. Units reflect toggles above.
Visualization
Bars show relative rate and time (normalized to Gas B = 1.0).
Common Gas Molar Masses
Click Use as A or Use as B to fill inputs.
Table applies to molar mass basis. In density mode, provide your measured ρ at the same T and P for both gases.
| Gas | M (g/mol) | Actions |
|---|---|---|
| Hydrogen (H₂) | 2.016 | |
| Helium (He) | 4.0026 | |
| Neon (Ne) | 20.1797 | |
| Nitrogen (N₂) | 28.0134 | |
| Oxygen (O₂) | 31.9988 | |
| Ozone (O₃) | 47.9982 | |
| Argon (Ar) | 39.948 | |
| Krypton (Kr) | 83.798 | |
| Xenon (Xe) | 131.293 | |
| Carbon monoxide (CO) | 28.0101 | |
| Carbon dioxide (CO₂) | 44.0095 | |
| Water vapor (H₂O) | 18.01528 | |
| Ammonia (NH₃) | 17.031 | |
| Methane (CH₄) | 16.043 | |
| Ethane (C₂H₆) | 30.07 | |
| Propane (C₃H₈) | 44.097 | |
| n-Butane (C₄H₁₀) | 58.12 | |
| Ethylene (C₂H₄) | 28.0532 | |
| Acetylene (C₂H₂) | 26.0373 | |
| Propylene (C₃H₆) | 42.0797 | |
| Ethanol (C₂H₆O) | 46.06844 | |
| Acetone (C₃H₆O) | 58.08 | |
| Benzene (C₆H₆) | 78.11184 | |
| Hydrogen chloride (HCl) | 36.46094 | |
| Hydrogen fluoride (HF) | 20.00634 | |
| Hydrogen bromide (HBr) | 80.91194 | |
| Hydrogen cyanide (HCN) | 27.0253 | |
| Nitric oxide (NO) | 30.0061 | |
| Nitrogen dioxide (NO₂) | 46.0055 | |
| Dinitrogen monoxide (N₂O) | 44.0128 | |
| Sulfur dioxide (SO₂) | 64.066 | |
| Sulfur hexafluoride (SF₆) | 146.06 | |
| Chlorine (Cl₂) | 70.906 | |
| Fluorine (F₂) | 37.9968 | |
| Bromine (Br₂) | 159.808 | |
| Iodine (I₂) | 253.80894 | |
| Phosgene (COCl₂) | 98.916 | |
| Formaldehyde (CH₂O) | 30.026 | |
| Hydrogen sulfide (H₂S) | 34.0809 |
Formula Used
Graham’s law (ideal gases, low pressure) states that the rate of diffusion/effusion of a gas is inversely proportional to the square root of its molar mass (M):
Rate ratio:
r_A / r_B = √( M_B / M_A )
Time ratio (same distance):
t_A / t_B = √( M_A / M_B )
Distance ratio (same time):
d_A / d_B = √( M_B / M_A )
Using density ρ at equal temperature and pressure is equivalent because ρ ∝ M via the ideal gas relation ρ = PM/RT, so the same square‑root ratios apply with ρ substituted.
Conditions & Non‑ideality Tips
- Use the same temperature and pressure for both gases to apply density mode correctly.
- At high pressures or for very polar/associating gases, deviations from √‑law may appear.
- Lowering pressure and working near room temperature improves ideal‑gas assumptions.
How to Use This Calculator
- Choose Molar mass or Gas density as the input basis.
- Pick gases from presets or enter values. In density mode, input ρ in kg/m³ or g/L at equal T and P.
- Optionally provide one time or one distance to compute its counterpart.
- Switch time and distance units; values convert instantly. The chart and results update live.
- Export CSV or PDF for records; include ambient temperature notes if relevant.
FAQs
At equal temperature and pressure, ρ ∝ M, so
r_A/r_B = √(ρ_B/ρ_A). This is algebraically identical to using molar masses.
Use densities measured or tabulated at the same T and P for both gases. Convert units to kg/m³ or g/L; they are numerically identical.
Ratios cancel T and P if both gases share the same conditions. If not equal, density mode is invalid; use molar masses instead.
Use molar mass when you have chemical identities; use density when you have experimental ρ values at equal T and P or need to validate with measured data.
Yes, exports include the selected input basis and the ambient temperature note for documentation.