partialpressure

Partial pressure is the pressure contribution of a single component gas within a mixture. It is defined as the pressure that that gas would exert if it occupied the entire volume at the same temperature, independent of the other components. In a gas mixture, each component has its own partial pressure, and the total pressure is the sum of all partial pressures.

In ideal gas mixtures, the partial pressure of a gas i is p_i = x_i P, where x_i is the mole fraction of that gas and P is the total pressure. Dalton's law states that the total pressure equals the sum of all partial pressures: P = ∑ p_i. Partial pressures are commonly expressed in units such as pascals (Pa), kilopascals (kPa), atmospheres (atm), or millimeters of mercury (mmHg).

Partial pressure has wide-ranging applications. In physiology, it helps describe gas exchange in the lungs and tissues; the oxygen partial pressure driving diffusion is a key parameter in respiratory physiology. In anesthesia and critical care, controlling inspired gas partial pressures (such as O2 and anesthetic agents) is essential. In environmental science and industrial processes, partial pressures determine the behavior of gas mixtures, including combustion and corrosion processes. Henry's law links partial pressure to dissolved gas concentration in liquids: C = k_H p, where C is the concentration and k_H is Henry’s constant.

Real gases depart from ideal behavior at high pressures or low temperatures, where interactions between molecules matter. In such cases, partial pressures remain well defined, but corrections via fugacity and virial or cubic equations of state may be used to account for non-ideality.