Gas Mixture Partial Pressure Calculator

Dalton's Law states that the total pressure of a mixture of non-reacting gases equals the sum of the partial pressures of each individual gas. Each gas in the mixture exerts pressure independently as if it alone occupied the entire volume. Mathematically: P_total = P₁ + P₂ + P₃ + ... = Σ Pᵢ

Partial pressure can be calculated using: Pᵢ = yᵢ × P_total, where yᵢ is the mole fraction of gas i. The mole fraction is calculated as yᵢ = nᵢ / n_total (moles of component i divided by total moles). Alternatively, if you know the volume and temperature, you can use the ideal gas law: Pᵢ = nᵢRT/V.

A mole fraction (y or χ) is the ratio of the number of moles of a component to the total number of moles in the mixture. It's a dimensionless quantity between 0 and 1, and all mole fractions in a mixture must sum to exactly 1. For example, if a mixture has 3 mol N₂ and 1 mol O₂, the mole fraction of N₂ is 3/4 = 0.75.

This follows from the ideal gas law and the assumption that gas molecules don't interact. Each gas molecule contributes to pressure through collisions with container walls, and these contributions are additive. The total pressure results from all molecular collisions combined, regardless of which gas species is involved.

Partial pressure refers to the pressure contribution of any gas component in a mixture. Vapor pressure specifically refers to the pressure exerted by a substance's vapor in equilibrium with its liquid or solid phase at a given temperature. Vapor pressure is a property of a pure substance, while partial pressure describes that substance's contribution when mixed with other gases.

Dalton's Law assumes ideal gas behavior and may not be accurate when: (1) gases are at very high pressures where molecular volumes become significant, (2) temperatures are very low (near condensation), (3) gases chemically react with each other, or (4) there are strong intermolecular forces between different gas species.

In respiration, partial pressures drive gas exchange. Oxygen moves from alveoli (P_O₂ ≈ 100 mmHg) to blood (P_O₂ ≈ 40 mmHg) because gases diffuse from high to low partial pressure. Similarly, CO₂ moves from blood to alveoli. Understanding these partial pressures is crucial for treating respiratory conditions.

Common pressure units include atmospheres (atm), kilopascals (kPa), bar, millimeters of mercury (mmHg), torr, and pounds per square inch (psi). The calculator supports multiple units, but ensure all partial pressures use the same units as the total pressure for consistency.

Use the formula: moles (n) = mass (m) / molar mass (M). For example, 28 g of N₂ (molar mass = 28.01 g/mol) equals approximately 1 mol. The calculator can derive moles from mass if you provide the molar mass for each component.

The consistency check verifies that the sum of calculated partial pressures (Σ Pᵢ) matches the given total pressure (P_total). A small deviation may occur due to rounding or measurement uncertainty, but large deviations (>1%) indicate possible input errors or that mole fractions don't sum to 1.