P

Partial Pressure

p_i = x_i × P_total; P_total = Σp_i
Quick Reference
Formula / Notationp_i = x_i × P_total; P_total = Σp_i
Also Known AsPartial pressure of gas, p_i, Dalton partial pressure, component pressure

What is Partial Pressure?

The pressure exerted by one component of a gas mixture as if it alone occupied the container. According to Dalton's law, the total pressure of a gas mixture equals the sum of partial pressures. Partial pressure is proportional to the mole fraction of each component.

Formula & Notation

p_i = x_i × P_total; P_total = Σp_i

Other Names / Synonyms: Partial pressure of gas, p_i, Dalton partial pressure, component pressure

Properties & Characteristics

Partial pressure is the pressure that each gas in a mixture would exert if it occupied the entire volume of the container alone at the same temperature. Dalton's law of partial pressures: the total pressure is the sum of the partial pressures: P_total = Σp_i = Σ x_i × P_total, where x_i is the mole fraction of gas i. For ideal gases, partial pressure is proportional to the mole fraction. Henry's law (gas solubility ∝ partial pressure) involves partial pressure.

Uses & Applications

Partial pressure is used in: calculating gas equilibrium constants Kp (expressed as dimensionless p/p° ratios), respiratory physiology (partial pressure of O₂ in lung alveoli drives gas exchange into blood: pO₂ = 13.3 kPa in alveoli), anaesthesia (minimum alveolar concentration is a partial pressure), and in industrial gas mixture specifications.

Safety Information

Oxygen partial pressure: deficiency (pO₂ < ~11 kPa) causes hypoxia; excess (pO₂ > ~140 kPa) causes oxygen toxicity (seizures, pulmonary damage in divers). Toxic gas partial pressures in mixtures determine their hazard: CO partial pressure of 0.1 kPa in a 1 atm atmosphere is acutely dangerous (≈ 1000 ppm).

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Partial Pressure
Formula p_i = x_i × P_total; P_total = Σp_i
Synonyms Partial pressure of gas, p_i, Dalton partial pressure, component pressure

Frequently Asked Questions

The pressure exerted by one component of a gas mixture as if it alone occupied the container. According to Dalton's law, the total pressure of a gas mixture equals the sum of partial pressures. Partial pressure is proportional to the mole fraction of each component.

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