With the same pressure and temperature, mole fraction and volume fraction are the same.

We can then use the molar mass of each gas and the fractions to calculate the average molar mass:

$\overline{){{\mathbf{MM}}}_{{\mathbf{ave}}}{\mathbf{}}{\mathbf{=}}{\mathbf{}}{{\mathbf{MM}}}_{{\mathbf{He}}}{{\mathbf{X}}}_{{\mathbf{He}}}{\mathbf{}}{\mathbf{+}}{\mathbf{}}{{\mathbf{MM}}}_{{\mathbf{CH}}_{\mathbf{4}}}{{\mathbf{X}}}_{{\mathbf{CH}}_{\mathbf{4}}}{\mathbf{+}}{\mathbf{}}{{\mathbf{MM}}}_{{\mathbf{N}}_{\mathbf{2}}}{{\mathbf{X}}}_{{\mathbf{N}}_{\mathbf{2}}}}$

An ideal gas mixture contains 35% helium, 20% methane, and 45% nitrogen (by volume) at 2.00 atm and 90°C. Calculate the average molecular weight of the gas mixture.

Frequently Asked Questions

What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the The Ideal Gas Law: Molar Mass concept. You can view video lessons to learn The Ideal Gas Law: Molar Mass. Or if you need more The Ideal Gas Law: Molar Mass practice, you can also practice The Ideal Gas Law: Molar Mass practice problems.