The Gas Laws Chapter 12

12.1 – Properties of Gases Kinetic Theory 3 main points 1.Gases consist of hard, spherical particles with negligible volume & empty space between them                                         

2. No attractive/repulsive forces b/w the particles & they are free to move in straight paths 3. They move rapidly in constant random motion & have elastic collisions with other gas particles

4 Variables that Describe Gases Pressure (P) in kilopascals (kPa) Volume (V) in liters (L) Temperature (T) in Kelvin (K) Number of Moles (n)

You will be able to predict the behavior of gases at specific conditions at the end of this chapter!!          

12.2 – Factors Affecting Gas Pressure 1. Collisions of gas particles with the inside walls of a container result in the pressure exerted by the gas

If you increase the amount of gas, you increase the # of collisions; therefore increasing the pressure If temperature remains constant, doubling the # of particles doubles the pressure (triple = triple, half = half, etc)

2. Gas will move from an area of high pressure to an area of low pressure 3. The volume of a gas will also affect the pressure

a. If you reduce the volume of gas, you raise the pressure b. If you increase the volume, you lower the pressure c. Doubling the volume will halve the pressure & vice versa

4. The temperature will affect the pressure a. If you raise the temperature, you increase the pressure

b. Speed & KE of gas particles will increase w/ increasing temp, & have more of an impact when they hit the walls of the container – increasing the pressure

c. Decreasing the temperature will decrease the pressure of the gas d. Halving the Kelvin Temperature will decrease the pressure by half

Boyle’s Law deals with the relationship between pressure & volume

When pressure goes up, volume goes down When pressure goes down, volume goes up We assume that temperature is remaining constant

Boyle’s Law states that if temperature and mass are constant, the volume of a gas varies inversely with the pressure of the gas

The formula for Boyle’s Law is: P1V1 = P2V2 That is: the initial pressure times the initial volume = the final pressure times the final volume

12.3 Charles’ Law Charles’ Law deals with the relationship between temperature and volume of a gas

As temperature goes up, volume goes up. As temperature goes down, volume goes down We assume pressure & mass are constant

Charles’ Law states that if pressure and mass are constant, the volume of a gas varies directly with the temperature of the gas

The formula for Charles’ Law is: V1 / T1 = V2 / T2 That is: the initial volume divided by the initial temperature (K) = the final volume divided by the final temperature (K)

12.3 Gay-Lussac’s Law Gay-Lussac’s Law deals with the relationship between temperature & pressure of a gas

As temperature goes up, pressure goes up As temperature goes down, pressure goes down We assume mass and volume are constant

Gay-Lussac’s Law states that if mass & volume are constant, the pressure of a gas is directly proportional to the Kelvin temperature of the gas

The formula for Gay-Lussac’s Law is: P1 / T1 = P2 / T2 The initial pressure divided by the initial temperature (K) = the final pressure divided by the final temp (K)

12.3 Combined Gas Law Sometimes pressure, volume and temperature are all changing (nothing constant except mass) There is a law we use when this occurs (much more common)

In a lab situation, we may assume a variable is held constant, but it can be really difficult to do so all the time The Combined Gas Law (CGL) is a combination of the other three

The formula for the CGL is: P1V1 / T1 = P2V2 / T2 Can you find Boyle’s Charles’ and Gay-Lussac’s Laws in the equation?

12.4 – Ideal Gas Law So far, we have only talked about temperature, pressure and volume, and have assumed mass stayed constant & therefore ignored it

When we are taking mass into consideration, we use number of moles (n) of gas We can add n to the CGL to get: P1V1 / T1n1 = P2V2 / T2n2

This shows that the ratio of PV / Tn (pressure times volume and temperature times moles) is a constant Ideal Gases hold true to this formula

Ideal Gases follow the Kinetic Theory – we know that no gases follow the Kinetic Theory however – therefore no gases are ideal – they are all real gases

Real gases do act like ideal gases in many situations (under certain temperatures and pressures) The ideal gas constant corrects for a real gas’ behavior

When we include R in the equation, we get the Ideal Gas Law R = PV / Tn OR PV = nRT (pivnert)

The ideal gas constant is called R = 8.314 (L x kPa) / (K x mol) 0.082 (L x atm) / (K x mol) 62.4 (L x mmHg)/(K x mol) Notice the different units!