TBS AP Chem: Dalton's Law of Partial Pressures

​The sum of the individual pressures of all the gases that make up a mixture is equal to the total pressure exerted by the mixture.

​The sum of the individual pressures of all the gases that make up a mixture is equal to the total pressure exerted by the mixture.

• The gas is collected by water displacement

• The gas is collec​ted over water

• ​The question asks about the "dry gas"

• ​The question gives you the vapor pressure of water

​For these problems, we often write the equation in this form:

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​where P_atm = P_tot

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​You will either be given the vapor pressure of water at that temperature or look it up online

​The mole fraction of A in a mixture is the moles of A divided by total moles

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Note: It is always expressed in decimal form with an appropriate number of significant figures.

The partial pressure exerted by an individual gas is equal to the mole fraction of the gas times the total pressure.