Gas Kinetic Molecular Theory Graham’s Law

Kinetic Molecular Theory The gas laws developed by Boyle, Charles, and Gay-Lussac, Avogadro are based upon the observable properties of gas (pressure, volume, temperature, amount) The observable properties of gas (pressure, volume, temperature) are the consequence of the actions of the molecules making up the gas To understand the behavior of a gas, we must look at the gas particles themselves link

Kinetic Molecular Theory The particles in a gas are considered to be small, hard spheres with an insignificant volume. –Gases are spread far apart, with empty space between molecules

Kinetic Molecular Theory The motion of the particles in a gas is rapid, constant, and random. –Gas takes the shape of its container and can spread out into space without limit –Particles change direction only when they rebound from collisions link

Kinetic Molecular Theory All collisions between particles in a gas are perfectly elastic. –No attractive or repulsive forces –No transfer of Kinetic Energy –The average Kinetic Energy is dependent only on Temperature

The average Kinetic Energy is dependent only on Temperature As the Temperature increases, the average kinetic energy (measured by speed), increases Maxwell Distribution Kinetic Molecular Theory

1.Gases are in constant, random motion. 2.Space between atoms considered negligible. 3.The energy for a sample of gas is considered constant. 4.Attractive and repulsive forces are negligible. 5.The kinetic energy of the molecules is proportional to the temperature.

Effusion Gas escaping into a vacuum Different than diffusion, although same trend/reasoning

Bigger means slower

Diffusion example

During an effusion experiment, Nitrogen effuses 1.73 times as fast as an unknown gas at the same conditions. What is the molar mass of the unknown gas? Graham’s Law of Effusion MW unk = g/mol

Graham’s Law of Effusion Compare the rates of effusion of N 2 and He. Therefore, Helium effuses 2.7 times as fast as N 2