If a mixture of gases with a total pressure of 1.0 atm contains 2 mol #He#, 4 mol #Ne#, and 2 mol #O_2#, what is the partial pressure of the #He# in the mixture?

1 Answer
Jan 19, 2016

Answer:

#"0.25 atm"#

Explanation:

The partial pressure of a gas that's part of a gaseous mixture will depend on two things

  • the mole fraction said gas has in the mixture
  • the total pressure of the mixture

As you know, Dalton's Law of Partial Pressures allows you to calculate the partial pressure of gas that's part of a gaseous mixture by using the number of moles of that gas and the total number of moles present in the mixture - this is known as the mole fraction

#color(blue)(P_i - chi_i xx P_"total")" "#, where

#P_i# - the partial pressure of gas #i#
#chi_i# - its mole fraction
#P_"total"# - the total pressure of the mixture

In your case, you know that the mixture contains

  • #"2 moles"# of helium
  • #"4 moles"# of neon
  • #"2 moles"# of oxygen gas

The *total number of moles8 present in the mixture will thus be

#n_"total" = 2 + 4 + 2 = "8 moles"#

The mole fraction of helium will be

#chi_(He) = (2 color(red)(cancel(color(black)("moles "))))/(8color(red)(cancel(color(black)("moles")))) = 1/4 = 0.25#

Therefore, the partial pressure of helium will be

#P_(He) = chi_(He) xx P_"total"#

#P_(He) = 0.25 xx "1.0 atm" = color(green)("0.25 atm")#

I'll leave the answer rounded to two sig figs.