http://www.ck12.org Chapter 14. The Properties of Gases
14.3 Gas Mixtures
Lesson Objectives
- Define partial pressure.
- Describe Dalton’s law of partial pressures and perform calculations using this equation.
- Define and perform calculations using mole fractions.
- Define diffusion and effusion and how they relate to other properties of gases.
Lesson Vocabulary
- partial pressure: The pressure that each individual gas exerts in a gaseous mixture.
- Dalton’s Law of Partial Pressures: States that if two or more gases are mixed in a container, each one will
exert the same amount of pressure that it would if it were by itself in a container of the same size. - mole fraction: Expresses what fraction or percentage a particular substance contributes to the total number of
gas particles present. - diffusion: When the random motions of gas particles in a large container results in an even distribution
throughout all the available space. - effusion: The process of a confined gas escaping through a tiny hole in its container.
- Graham’s law of effusion: States that the rate of effusion or diffusion of a gas is inversely proportional to the
square root of the molar mass of the gas.
Check Your Understanding
- Which of the following statements are true about gases?
a. Gases always form a solid coating on the interior of the container which they are bounded by.
b. Gas particles move fairly quickly, often at speeds of more than 100 miles per hour.
c. In environments with multiple gases, there will be two layers formed –the heaviest gases on the bottom,
lightest on top.
d. Gases mix homogeneously, regardless of which gases are combined.
Introduction
In our previous lesson, we studied the relationships that exist between pressure, temperature, volume, and amount
for gases. One assumption we made was that the gases behave ideally, which means that the collisions between
gas particles are completely elastic, the particles do not attract or repel one another, and the particle volumes are
negligible compared to the overall volume that they occupy. Many properties of ideal gases do not depend on the
identity of the gas. For example, we know that one mole of any ideal gas takes up 22.4 L at STP, regardless of the