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Partial PressurePressure of individual gases in a mixture

Daltons’ Law of Partial PressuresThe total pressure inside a container is

equal to the partial pressure due to each gas.

The partial pressure is the contribution by that gas.

PTotal = P1 + P2 + P3

2 atm

1 atm

3 atm

6 atm

ExamplesWhat is the total pressure in a balloon filled

with air if the pressure of the oxygen is 170 mm Hg and the pressure of nitrogen is 620 mm Hg?

In a second balloon the total pressure is 1.3 atm. What is the pressure of oxygen if the pressure of nitrogen is 720 mm Hg?

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More ExamplesWhat pressure is exerted by a mixture of

2.00 g of hydrogen gas and 8.00 g of nitrogen gas at 273 K and in a 10.0 L vessel?

If a .20 L sample of oxygen at 0°C and 1 atm and a .10 L sample of nitrogen at 0°C and 2.0 atm are both placed in a .40 L container at 0°C, what is the total pressure of the mixture?

Ratio of the number of moles of a component in a mixture to the total number of moles in the mixture

Numerically equal to the ratio of the partial pressure of a component gas to the total pressure of the gas mixture

Mole Fraction

2 2

total total

n P

n P

The partial pressure of oxygen was observed to be 156 torr in air with a total atmospheric pressure of 743 torr. Calculate the mole fraction of oxygen in the sample.

Example

Gas Collection

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Gas Collection

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When a gas is collected over water, water vapor ends up in the gas

The pressure of the pure gas is the total pressure minus the pressure of the water vapor Ptot = Pgas + Pwater

Pgas = Ptot - Pwater

Water Vapor Pressure

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Pressure of the water vapor depends on the temperature at which the gas is collected

Example

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Carbon dioxide gas is collected over water at a temperature of 18°C. The barometric pressure reads 775 mm Hg. What is the pressure of the carbon dioxide?