Chapter 12 Notes, Part II Ideal Gas Law Dalton’s Law of Partial Pressures Graham’s Law of Effusion

Ideal Gas Law When a gas behaves ideally (that is, it obeys the assumptions about gases in the kinetic theory) then it is possible to use the ideal gas law to define it.

Ideal Gas Law The equation is: PV=nRT Pressure x vol. = # of moles x ideal gas constant x temp.

Ideal Gas Law The letter R is the ideal gas constant. R’s value is 8.31 L kPa / mol K

Ideal Gas Law Two factors make a gas not ideal; the fact that the particles will interact and that they do have volume. Because of this, the relationship breaks down at very high pressures and very low temperatures.

Practice Problem #1 You fill a rigid container that has a volume of 20.0L with nitrogen gas to a pressure of 2150 kPa at 28oC. How many moles of gas are present?

Practice Problem #2 What volume will 12 grams of oxygen gas (O2) will occupy at 25oC and 52.7 kPa?

Dalton’s Law of Partial Pressures Avogadro's hypothesis-identical volumes of gas at the same temperature and pressure have the same number of particles, regardless of the type of gas!

Dalton’s Law of Partial Pressures Based on this, Dalton could say that the total pressure in a container is equal to the sum of the pressures of a mixture of gases.

Dalton’s Law of Partial Pressures Ptot=P1+P2+P3...

Practice Problem #3 Air contains oxygen, nitrogen, carbon dioxide and trace amounts of other gases. What is the partial pressure of oxygen at 101.3kPa if the partial pressures of nitrogen, carbon dioxide and other gases are 79.1kPa, 0.040 kPa and 0.94kPa, respectively?

Practice Problem #4 What is the total pressure in a container where the partial pressures are as follows: Nitrogen—20.0kPa Oxygen—37.2kPa Helium 19.1kPa

Graham’s Law Diffusion-the tendency of molecules to move toward areas of low concentration until the concentration is uniform throughout.

Graham’s Law Graham studied effusion, or diffusion through a tiny hole in a container. He noticed that the heavier the molecules in the gas, the longer it took for them to diffuse.

Graham’s Law He came up with the relationship between two gases (gas A and gas B) to be: RateA molar massB RateB molar massA =

Practice Problem #5 How much faster will methane (CH4) diffuse throughout the room than argon?

Practice Problem #6 It takes 10 minutes for oxygen gas to completely diffuse from its container into the room. How fast would the gas have diffused if it was helium?