Gas Mixture Calculator (Dalton’s Law)
Compute partial pressures, mole fractions, and total pressure for ideal gas mixtures. Build custom blends or analyze existing mixtures in one place.
Gas mixture calculator
Gas components
| Gas name | Partial pressure | Mole fraction | Remove |
|---|
Results
Mixture summary
Total pressure:
Number of components:
Checks
Sum of mole fractions:
Assumes ideal gas behavior (Dalton’s law). For high pressures or strong interactions, real-gas corrections may be needed.
| Gas | Partial pressure | Mole fraction |
|---|
How the gas mixture calculator works
This tool uses Dalton’s law of partial pressures for ideal gases. It lets you:
- Start from partial pressures and get mole fractions and total pressure.
- Start from moles or mole fractions and get mole fractions and, if total pressure is known, partial pressures.
- Quickly build common mixtures such as dry air.
Key formulas
Dalton’s law of partial pressures
\[ P_\text{total} = \sum_i P_i \]
Mole fraction of component \(i\)
\[ y_i = \frac{n_i}{\sum_j n_j} \]
Relation between partial pressure and mole fraction
\[ P_i = y_i \, P_\text{total} \]
For ideal gases at the same temperature and volume, the ratio of partial pressures equals the ratio of moles:
\[ \frac{P_i}{P_j} = \frac{n_i}{n_j} \]
Example: approximate composition of dry air
At 1 atm, a typical dry air mixture is:
- N2: 0.7808 mole fraction → 0.7808 atm
- O2: 0.2095 mole fraction → 0.2095 atm
- Ar: 0.0093 mole fraction → 0.0093 atm
- CO2: 0.0004 mole fraction → 0.0004 atm
Click “Load dry air example” to see these values pre-filled and explore how the calculator handles them.
When is the ideal gas assumption reasonable?
Dalton’s law assumes an ideal gas mixture, which is usually a good approximation at:
- Moderate pressures (around 1 atm).
- Temperatures well above the gases’ boiling points.
- Weakly interacting gases (e.g., air components).
At very high pressures, very low temperatures, or for strongly interacting gases, you may need real-gas models (e.g., virial equation, cubic equations of state) and activity coefficients.
Gas mixture FAQ
What is a gas mixture?
A gas mixture is a combination of two or more gases occupying the same volume. Each gas behaves as if it alone occupied the container (for ideal gases), and its contribution to the total pressure is called its partial pressure.
What is partial pressure?
The partial pressure of a gas in a mixture is the pressure it would exert if it alone occupied the container at the same temperature. For ideal gases, \( P_i = y_i P_\text{total} \), where \( y_i \) is the mole fraction of gas \(i\).
Can I use this for gas blending (e.g., scuba, welding, shielding gases)?
Yes, as a first approximation. The calculator is ideal-gas based and works well for moderate pressures. For high-pressure cylinders or safety-critical breathing mixtures, always follow your industry’s detailed blending procedures and standards.
What units does the calculator support?
You can work in atm, kPa, mmHg, or psi. Internally, all pressures are converted to atm for calculations and then converted back to your chosen unit for display.