Question

26.

Learning Goal:

To use partial pressure in gas law calculations.

In a mixture of gases, the total pressure of the gas mixture is equal to the sum of the partial pressures of the individual gases. For example, if you have a mixture of helium at 2 atmand argon at 4 atm , then the total pressure of the gas inside the cylinder is 6 atm . (Figure 1)
Similarly, if you know the total pressure of a gas mixture, you can use the number of moles to find the partial pressures, or the partial pressures to find the number of moles.

Example Problem: A mixture of N2, O2, and He gases has a total pressure of 1 atm . The partial pressures of N2 and O2are 0.7 atm and 0.25 atm , respectively. What is the partial pressure of He?
The sum of the partial pressures is equal to the total pressure:

Ptotal=PN2+PO2+PHe

Rearranging this equation, the partial pressure of He is

PHe===Ptotal−PN2−PO21.00atm−0.70atm−0.25atm0.05atm

A. A mixture of He, Ar, and Xe has a total pressure of 2.30 atm . The partial pressure of He is 0.450 atm , and the partial pressure of Ar is 0.300 atm . What is the partial pressure of Xe?

Express your answer to three significant figures and include the appropriate units.

Answer 1

Total pressure of gases mixture = sum of partial pressure of each gas = p_He + p_Ar + p_Xe

= 0.450atm + 0.300atm + p_Xe = 2.30atm

p_Xe = 2.30atm - 0.750atm = 1.55atm

Partial pressure of Xe = 1.55atm . (Answer)