8.4 The Kinetic Molecular Theory and Real Gas Behavior

Kinetic Energy of Gas Particles

Root Mean Square Velocity

Effusion and Diffusion Diffusion is the term used to describe the mixing of one gas through another. The rate of diffusion is the rate of this mixing. The rate of diffusion is calculated by directly relating the relative distance travelled by two types of molecules in the same period of time to their relative velocities. Both of these ratios are inversely related to the square root of the ratio of the molecules’ masses. Effusion is the passage of a gas through a tiny orifice into an evacuated chamber. The rate of effusion measures the speed at which the gas is transferred into the chamber.

The E ff ects of Volume and Intermolecular Forces on Real Gases In section 8.2 it was stated that gases behave most ideally when pressure is low and temperature is high. The reason for this is two-fold: 1.Real gases do have some volume, while ideal gases are assumed to have no volume and to exist as tiny points in space. 2. Real gases exert some attractive forces on their neighbouring particles, while ideal gases are assumed to be completely independent of the gas particles that surround them. In 1873, Johannes van der Waals modified the ideal gas law to fit the behaviour of real gases. The “correction factors” include an a factor and a b factor, which account for the attractive forces and the volume that real gases demonstrate. Every gas has its own unique values for a and b. Note that the units of a and b allow proper cancellation to produce units of pressure and volume respectively when substituted into the van der Waals equation.