• id: JTHERM-02-N10
• title: Pressure in Gas Mixtures
• tags: dalton, partial-pressure, mixture

In a mixture of non-reacting ideal gases, each gas exerts pressure independently as if the other gases were absent. The total pressure equals the sum of partial pressures: $P_{\text{total}} = P_1 + P_2 + \ldots$ Partial pressure of gas $i$: $P_i = n_iRT/V = x_iP_{\text{total}}$, where $x_i = n_i/n_{\text{total}}$ is the mole fraction. This follows directly from kinetic theory — molecules of different species don't interact (ideal gas assumption), so their contributions to momentum transfer (and hence pressure) are additive. Dalton's law fails for real gas mixtures at high pressures where intermolecular interactions are significant.