Partial Pressure
Calculate the partial pressure of any gas in a mixture using Dalton's law: partial pressure = mole fraction × total pressure. Free online chemistry calculator with charts and breakdowns.
About This Calculator
The Partial Pressure Calculator helps chemistry students, lab professionals, and researchers determine the pressure exerted by an individual gas in a mixture using Dalton's law. Partial pressure is essential for understanding gas behavior in chemical reactions, respiratory physiology, gas collection experiments, and industrial gas processing.
How Partial Pressure Works — Dalton's Law
Dalton's law of partial pressures states that the total pressure exerted by a mixture of non-reacting gases equals the sum of the partial pressures of each individual gas. The partial pressure of a specific gas is calculated by multiplying its mole fraction by the total pressure: Pi = xi × Ptotal. The mole fraction (xi) is the ratio of the number of moles of that gas to the total number of moles in the mixture.
Formula
Pi = (ni / ntotal) × Ptotal
Where Pi is the partial pressure of gas i, ni is the moles of gas i, ntotal is the total moles of all gases, and Ptotal is the total pressure of the mixture.
Applications of Partial Pressure
Breathing & Respiratory Physiology: In medicine, partial pressure of oxygen (PaO₂) and carbon dioxide (PaCO₂) are critical measurements in arterial blood gas analysis. The partial pressure of oxygen in atmospheric air at sea level is approximately 0.21 atm (21% of 1 atm).
Scuba Diving: Divers must monitor partial pressures of oxygen and nitrogen to avoid oxygen toxicity and decompression sickness. The partial pressure of oxygen increases with depth, making oxygen-enriched mixtures dangerous below certain depths.
Chemical Reactions: In gas-phase reactions, equilibrium constants (Kp) are expressed in terms of partial pressures. Understanding partial pressures is critical for calculating reaction yields and optimizing industrial processes like the Haber-Bosch process for ammonia synthesis.
Gas Collection: When collecting gases over water, the total pressure includes the vapor pressure of water. Dalton's law allows correcting for water vapor to find the pressure of the dry gas alone.
Regional Notes
This calculator uses atmospheres (atm) as the pressure unit, which is the standard unit for Dalton's law calculations worldwide. For conversion: 1 atm = 101.325 kPa = 760 mmHg = 1.01325 bar. The mole and atmosphere are SI-accepted units used universally in chemistry regardless of region.
Frequently Asked Questions
What is partial pressure and Dalton's law?
Partial pressure is the pressure that a single gas component exerts in a mixture of gases. Dalton's law states that the total pressure of a gas mixture equals the sum of the partial pressures of each individual gas. Mathematically, P_total = P_1 + P_2 + ... + P_n, and the partial pressure of a gas equals its mole fraction multiplied by the total pressure.
How do I calculate partial pressure from moles?
First, find the total number of moles by adding the moles of all gases. Then, calculate the mole fraction of the gas of interest by dividing its moles by the total moles. Finally, multiply the mole fraction by the total pressure to get the partial pressure: P_i = (n_i / n_total) × P_total.
What units does this partial pressure calculator use?
This calculator uses atmospheres (atm) for pressure and moles (mol) for the amount of gas. Results are displayed to four decimal places for precision. You can convert atm to other units like kPa (1 atm = 101.325 kPa) or mmHg (1 atm = 760 mmHg) if needed.
Can I use this calculator for gas mixtures with more than two gases?
This calculator is designed for binary gas mixtures. For mixtures with three or more gases, you can group the remaining gases as 'Gas 2' by summing their moles together. The partial pressure of Gas 1 will still be calculated correctly using P_1 = (n_1 / n_total) × P_total.
Is this partial pressure calculator free to use?
Yes, this partial pressure calculator is completely free to use with no registration or hidden charges. You can bookmark or share your calculation results via the URL, which saves all your input values.
What is the mole fraction and how is it related to partial pressure?
The mole fraction (x_i) is the ratio of the number of moles of a specific gas to the total number of moles of all gases in the mixture. Dalton's law shows that the partial pressure of a gas is directly proportional to its mole fraction: P_i = x_i × P_total. If the mole fraction is 0.5, the gas contributes 50% of the total pressure.