PV = nRT is an equation, and it can be manipulated just like all other equations. With this in mind, let's see how the ideal gas law can help us calculate gas density.
Density d has the units of mass over volume. The ideal gas law transforms into a form with units in mol per unit volume:
|d = =|
Dalton's law states that the total pressure of a mixture of gases is the sum of the pressures each constituent gas would exert if it were alone. Dalton's law can be expressed mathematically:
|P tot = P A + P B + P C + ...|
Each individual gas obeys the ideal gas law, so we can rearrange PV = nRT to find pressure:
|P A = n a|
Dalton's law problems often present two containers of gas, mix them, and ask you to find the partial pressures of each gas. There's usually an easy way and a hard way to do such problems; the trick is finding the easy way. You'll gain this intuition quickest if you jump right in. Try your hand at the problems at the end of this section and in your textbook.
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