Enter the total pressure and mole fraction of a component to calculate its partial pressure. The partial pressure is calculated through the use of Dalton’s law of partial pressures. This calculator can also determine the mole fraction or total pressure given the other values.
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Partial Pressure Formula
The following formula is used by the calculator to evaluate the partial pressure of a substance.
PP = TP * Mole Fraction
- Where PP = partial pressure
- TP = total pressure
- Mole Fraction is the fraction of the total moles made up by the substance (0 to 1, inclusive)
To calculate a partial pressure, multiply the total pressure by the mole fraction.
Partial pressure can also be found using the ideal gas law (for ideal mixtures, Pi = niRT/V). In solutions, Henry’s law relates a gas’s partial pressure to its dissolved concentration (depending on the form/units of the Henry’s law constant).
Partial Pressure Definition
Partial pressure is a term used to describe the portion of the total pressure contributed by one component in a gas mixture. Perhaps, we should take a step back. Pressure is force per unit area exerted on a surface. In the case of a gas in a container, gas molecules collide with the walls and exert forces on them, producing pressure.
Partial pressure is the pressure contribution from a single component compared to the total pressure of the mixture. In an ideal gas mixture, a component’s partial pressure is proportional to its mole fraction (the ratio of its moles to the total moles). This means if we know the fraction of the moles of the substance to the total moles, we can multiply it by the total pressure to get the partial pressure.
How to calculate partial pressure?
The following example goes over how you determine the partial pressure of a substance in an ideal gas. Let’s assume that gas is comprised of 3 different substances, oxygen, nitrogen, and helium. We want to know the partial pressure that oxygen exerts compared to the total pressure.
- First, we must measure the total pressure. This can be done using several measurement devices, but for this example, we will assume we know it’s 200 psi.
- Next, we need to determine the mole fraction of oxygen compared to the total moles. Suppose the mixture contains 200 moles of oxygen, 200 moles of nitrogen, and 200 moles of helium (600 total moles). Therefore the mole fraction of oxygen is 200/600 = 1/3.
- Finally, plug in all of the numbers into the equation above. PP = TP * 1/3 = 200 psi * 1/3 = 66.67 psi.
- Analyze the results and adjust the calculation.
As mentioned previously, the partial pressure can also be calculated through the use of the ideal gas law. From P = nRT/V, pressure is directly proportional to temperature and number of moles, and inversely proportional to volume. Therefore, if you enter the number of moles of your specific substance (and you know the volume and temperature of the gas mixture), you can calculate that component’s partial pressure as Pi = niRT/V (assuming ideal-gas behavior).
FAQ
Partial pressure is a term used to describe the portion of the total pressure contributed by one component in a gas mixture.
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