When a container is filled with 3.00 moles of H_2, 2.00 moles of O_2, and 1.00 mole of N_2, the pressure in thecontainer is 768 kPa. What is the partial pressure of O_2?

1 Answer

Partial Pressure of O_2 = 256 kPa.

Dalton's law of partial pressures covers two concepts;

  • Mole fraction
  • Partial pressure

Let's talk about Mole Fraction first.

You have a mixture of H_2, O_2 and N_2 in the container. The mole fraction of gas O_2 is worked out by dividing the number of moles of gas O_2 by the total number of moles of gas.

chi_(O_2) = ("number of moles of gas" O_2)/("total number of moles of gas")

chi_(O_2) = (2cancel("moles"))/((3+2+1)cancel("moles")) = 1/3

Next, the equation of the partial pressure of a gas can be written as;

P_(O_2) = "mole fraction of " O_2 xx "Total Pressure"

Since now we know the mole fraction of O_2, and the total pressure, we can just substitute the values into the partial pressure equation.

P_(O_2) = 1/3 * "768 kPa" = "256 kPa"

Note:

The total pressure can be calculated using this;

P_"total" = P_"gas A" + P_"gas B" + P_"gas C" +...