Unit 7 Gases

Gas Properties Video 7.1

Kinetic Molecular Theory Review Ideal Gases are perfect gases. They have: No mass No volume No attractive forces When will real gases behave this way? When they are spread out Temperature is high Pressure is low

Boyle’s Law Pressure and volume have an indirect relationship. P1V1=P2V2 What happens to a balloon if you put pressure on it? If you release it into the atmosphere?

Charles’ Law Volume and temperature have a direct relationship. V1/T1 = V2/T2 What happens to a car tire in the winter?

Gay-Lussac’s Law Pressure and temperature have a direct relationship. P1/T1 = P2/T2

Combined Gas Law Video 7.2

Combined Gas Law P1V1 = P2V2 T1 T2 Only used when discussing initial and final conditions of a gas. If something is held constant, cross it out of the equation. Temperature must be in Kelvin!

Question 1 P1V1 = P2V2 T1 T2 P1V1 = P2V2 (5.6x103)(1.53) = (1.5x104)(x) X = .571 L

Question 2 A 32.9L sample of a gas at constant pressure increases in temperature from 25 to 45C. Should the volume increase or decrease? Calculate the new volume. P1V1 = P2V2 T1 T2 V1 = V2 T1 T2 32.9 = x . 298 318 X= 35.1 L

Question 3 A gas in a rigid container has a pressure of 3.5 atmospheres at 200K. Calculate the pressure at 273K. P1V1 = P2V2 T1 T2 P1 = P2 T1 T2 3.5 = x . 200 273 X = 4.78 atm

Other Gas Laws Video 7.3

Avogadro’s Law Two different gases as the same temperature, volume, and pressure have the same number of molecules.

Graham’s Law of diffusion Gases move from high to low concentrations. Lighter gases diffuse faster. Which diffuses the fastest: He or N2? Why will F2 and Ar diffuse at almost the same rate?

Graham’s Law of diffusion

Dalton’s Law of partial pressures The total pressure in a system of gases equals the pressure of each individual gas combined.

Example 1. If the total pressure of a container of gases is 3 atmospheres and it contains 1 atmosphere of oxygen, 0.5 atm of nitrogen, 0.75 atm of methane, what is the partial pressure of the remaining gas? 3 – 1 - .5 - .75 = .75 atm

Harder Example PNe= (4.46/7.35)(2) = 1.21 atm 2. A mixture of gases contain 4.46 moles Ne, 0.74 moles of Ar, and 2.15 moles of Xe. Calculate the partial pressure of each gas if the total pressure is 2 atm. PNe= (4.46/7.35)(2) = 1.21 atm PAr= (0.74/7.35)(2) = 0.201 atm Pxe= (2.15/7.35)(2) = 0.585 atm

Class Notes

How do we breathe?

Why is Boyle’s law important to scuba divers?

Why is Charles’ Law important in hot air ballooning?

The general-purpose tank car in the photo before was being steam cleaned in preparation for maintenance.  The job was still in progress at the end of the shift so the employee cleaning the car decided to block in the steam.  The car had no vacuum relief so as it cooled, the steam condensed and the car imploded.