Engineering Calc Tools

Thermodynamics

Ideal Gas Mixture Calculator

Mole and mass fractions, apparent molar mass, gas constant, c_p, k and partial pressures of an ideal-gas mixture.

Tool no.
ECT-T11
Rev
1.0
Updated
Oct 2026
Method
Dalton and Amagat laws
Examples

Given

Formula and amount, for example N2 0.79. Gases: N2, O2, Ar, CO2, CO, H2O, H2, He, CH4, C2H6, C3H8, C4H10, NH3, SO2, Ne, air.

Leave blank if you only need properties.

Answers

Apparent molar mass M =—
Runs in your browser. Nothing you enter is uploaded.M = ΣyiMi · Pi = yiP
How to use this calculator

List each gas with its amount and say whether the amounts are mole fractions, mass fractions, moles or masses. Fractions don’t have to add to exactly 1: they are normalized. Add the pressure and temperature for partial pressures, density and volume.

Formulas

Mole fractionyi = Ni/N
Molar massM = ΣyiMi = 1/Σ(mfi/Mi)
Conversionmfi = yiMi/M
DaltonPi = yiP
Mixture cpcp = Σmficp,i

Worked example

Çengel 13-4: 3 kg O₂, 5 kg N₂ and 12 kg CO₂ at 300 kPa and 27 °C

  1. Moles: 3/32 = 0.0938, 5/28 = 0.1786, 12/44 = 0.2727 kmol; total N = 0.545 kmol.
  2. M = m/N = 20/0.545 = 36.7 kg/kmol, so R = 8.314/36.7 = 0.2265 kJ/kg·K.
  3. Mole fractions 0.172, 0.328, 0.500; the CO₂ partial pressure is 0.500 × 300 = 150 kPa.
  4. V = mRT/P = 20 × 0.2265 × 300/300 = 4.53 m³.

Frequently asked questions

When do I use mole fractions and when mass fractions?

Pressures and volumes follow mole fractions (Dalton and Amagat). Mass-specific properties such as cp in kJ/kg·K are averaged with mass fractions.

Is the mixture’s k the average of the k values?

No. Average cp and cv on the same basis first, then take k = cp/cv.