Dalton's Law of Partial Pressure

Dalton’s Law of Partial Pressures states:

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.

Formula: P${}_{tot}$ = P${}_1$ + P${}_2$ + P${}_3$ …

(as long as same temp and volume)

Clues when to use Dalton’s Law §

• The gas is collected by water displacement
• The gas is collected over water
• The question asks about “dry gas”
• The question gives you the vapor pressure of water

Mole Fraction §

To find partial pressure exerted by individual gas A use:

P${}_A$ = $\frac{molesA}{totalmoles}$ * P${}_{tot}$