5.7.3

Partial Pressures

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Partial Pressures of Gases

If you have a mixture of gases, you can split the total pressure into the pressures of each individual gas.

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Partial pressures

  • Say you have a 50/50 mix of water vapor and nitrogen gas at a pressure of 1 bar.
  • You can split this into a partial pressure for water vapor and nitrogen gas.
    • This follows from the ideal gas law. This states that every gas occupies the same volume under the same conditions.
  • We would say that the water vapor has a partial pressure of 0.5 bar and the nitrogen gas has a partial pressure of 0.5 bar.
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A different mixture

  • If we had a 75/25 mixture of oxygen and argon at a pressure of 1 bar, we would say that:
    • The partial pressure of oxygen is 0.75 bar.
    • The partial pressure of argon is 0.25 bar.
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Mole fractions

  • Another way to think about this is using mole fractions.
  • If you have 3 moles of oxygen gas and 2 moles of nitrogen gas, you can define a mole fraction of oxygen and nitrogen.
    • The mole fraction of oxygen is ⅗.
    • The mole fraction of nitrogen is ⅖.
  • If you multiply the mole fraction by the total pressure, you get the partial pressures of the gases.

Jump to other topics

1Structure - Models of the Particulate of Matter

2Structure - Models of Bonding & Structure

3Structure - Classification of Matter

3.1The Periodic Table: Classification of Elements

3.2Periodic Trends

3.3Group 1 Alkali Metals

3.4Halogens

3.5Noble gases, group 18

3.6Functional Groups: Classification of Organic

3.7Functional Group Chemistry

3.8Alkanes

3.9Alcohols

3.10Halogenoalkanes

4Reactivity - What Drives Chemical Reaction?

5Reactivity - How Much, How Fast & How Far?

6Reactivity - The Mechanisms of Chemical Change

7Measurement, Data Processing & Analysis

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