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

A quick word on moles… We will talk about moles much more in depth, but for now, know that it measures AMOUNT of substance—not volume or mass, but amount.

Like… Brace, pair, couple = 2 Dozen = 12 Bakers’ dozen = 13 Score = 20 Gross = 144 (12 dozen) Great gross = 1728 (12 gross) 1 mole = 6.02x10 23

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.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: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.The letter R is the ideal gas constant. R’s value is 8.31 L kPa / mol KR’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.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.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 28 o C. How many moles of gas are present?You fill a rigid container that has a volume of 20.0L with nitrogen gas to a pressure of 2150 kPa at 28 o C. How many moles of gas are present?

Practice Problem #2 What volume will 1.2 moles of oxygen gas (O 2 ) will occupy at 25 o C and 52.7 kPa?What volume will 1.2 moles of oxygen gas (O 2 ) will occupy at 25 o C 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!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.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. Another way to look at it is that in a mixture of gases, the type of gas doesn’t matter, the amount of gas determines the pressure.Another way to look at it is that in a mixture of gases, the type of gas doesn’t matter, the amount of gas determines the pressure.

Dalton’s Law of Partial Pressures P tot =P 1 +P 2 +…P n

Practice Problem #3 What is the total pressure in a container where the partial pressures are as follows:What is the total pressure in a container where the partial pressures are as follows: –Nitrogen—20.0kPa –Oxygen—37.2kPa –Helium 19.1kPa

Practice Problem #4 A mixture of 1mol oxygen, 2mol helium and 3mol carbon dioxide are in a canister. If the total pressure is 250kPa, what is the pressure due to just helium?A mixture of 1mol oxygen, 2mol helium and 3mol carbon dioxide are in a canister. If the total pressure is 250kPa, what is the pressure due to just helium?