Convert mass flow to molar flow, or molar flow to mass flow, using a supplied molar mass. Keep the substance or mixture basis explicit, distinguish mol from kmol and lbmol, and follow the normalized calculation steps.
02 Read the converted flow
Molar flow rate · ṅ
kmol/h
Enter flow and molar mass to begin.
- Molar mass · M
- Unit check
- Mass flow · ṁ
- Molar flow · ṅ
The molar mass must match the specified entities and the component or total-mixture stream basis.
03 Trace the mass–amount relation
Formula and method
Molar mass is mass per amount of substance, M = m/n. For the same stream and chemical-entity basis, molar flow ṅ = ṁ/M and mass flow ṁ = ṅM.
The engine normalizes mass flow to kg/s, molar flow to mol/s, and molar mass to kg/mol. Dividing kg/s by kg/mol gives mol/s; multiplying mol/s by kg/mol gives kg/s. The chosen output unit then sets the amount or mass scale and the time basis.
Molar-mass and flow units
| Quantity | Unit basis |
|---|---|
| Mass flow | kg/s, kg/min, kg/h, t/h, lbm/s, lbm/min, lbm/h |
| Molar flow | mol, kmol, or lbmol per s, min, or h |
| Molar mass | g/mol, kg/kmol, kg/mol, lbm/lbmol |
1 kmol = 1000 mol and 1 lbmol = 453.59237 mol. Here lbm is the international avoirdupois pound, 0.45359237 kg, and t is a metric tonne, 1000 kg. One minute is 60 s and one hour is 3600 s.
Molar-mass values in g/mol, kg/kmol, and lbm/lbmol have the same numerical value: 18 g/mol = 18 kg/kmol = 18 lbm/lbmol = 0.018 kg/mol. A mol-to-kmol change contributes a factor of 1000; do not drop it when mixing kg/mol with kg/kmol. Enter a dimensional molar mass, not an unlabelled relative molecular mass.
Component and mixture basis
- One species or component: use the flow of that species with its molar mass. Specify the same molecules, atoms, ions, or formula units in the amount basis and molar mass. A total mixture flow cannot be converted using just one component’s molar mass.
- Total mixture flow: supply the mean molar mass of that same mixture and composition basis. From mole fractions, M̄ = ΣxᵢMᵢ; from mass fractions, M̄ = 1 / Σ(wᵢ/Mᵢ), with fractions summing to 1 and consistent molar-mass units. The converter does not calculate composition or mean molar mass.
- Use matching wet/dry, phase, and stream definitions. Reactions or changing composition can change the appropriate mean molar mass. The conversion is an algebraic relation for the supplied basis, not a material-balance or reaction calculation.
Assumptions and limits
- Molar mass must be positive. Flow is a nonnegative magnitude; zero produces zero mass and molar flow. Assign signs separately when placing a stream in a material balance.
- No compound, atomic-weight, isotope, or composition database is used. The molar mass is your explicit input. The example value is illustrative and does not declare an exact property of water or another substance.
- No density, gas temperature, pressure, or compressibility is inferred. Converting volumetric or standard gas flow requires a separate property/state calculation.
- Arithmetic uses double precision. Results display up to 8 significant digits, steps up to 10. Normalized molar mass, mass flow, molar flow, and output must be finite and representable; overflow and nonzero underflow are rejected.
Worked examples
Mass to molar flow: take 1800 kg/h and a supplied M = 18 g/mol = 0.018 kg/mol. Normalize ṁ = 1800/3600 = 0.5 kg/s. Then ṅ = 0.5/0.018 = 27.77777778 mol/s, or 100 kmol/h. Reversing 100 kmol/h with the same M returns 1800 kg/h.
Imperial basis: 100 lbm/h divided by 20 lbm/lbmol gives 5 lbmol/h, or 2267.96185 mol/h. The molar flow is not 5 mol/h. Changing units preserves the physical flow and molar mass; changing direction carries the last valid result into the new input.
Mixture basis: a hypothetical 50 mol% mixture of species with M₁ = 20 g/mol and M₂ = 40 g/mol has M̄ = 30 g/mol. A total flow of 300 kg/h is therefore 10 kmol/h. A 50 mass% mixture of the same species instead has M̄ = 26.66666667 g/mol and 11.25 kmol/h; the fraction basis matters.
Sources and calculation version
- NIST SP 811, Chapter 8, section 8.6.4 — molar mass M = m/n in kg/mol, and mean molar mass for mixtures.
- NIST: SI Units – Amount of Substance — the mole and the need to specify the elementary entities.
- QUDT Units Vocabulary: Pound Mole — lbmol-to-mol conversion. Mass and time factors follow NIST SP 811, Appendix B.9.
Changelog: engine 1.0.0 introduces bidirectional mass/molar flow, explicit dimensional molar mass, SI normalization, component/mixture basis notes, unit conversion, zero flow, examples, and range checks. Shared mass/time factors 1.0.0 and amount/molar-mass definitions 1.0.0 are versioned locally. No chemical-property dataset is used. Engineering review status: independent review pending.