Chapter 6 1

Properties of Gases• Expand to completely fill their container• Take the shape of their container• Low density

– Much less than solid or liquid state

• Compressible• Mixtures of gases are always homogeneous• Fluid

Chapter 6 2

Gas Laws – Kinetic Molecular Theory

1. All matter is composed of tiny discrete particles called molecules

2. Molecules in a gas are in rapid constant motion and move in straight lines

3. Molecules of a gas are tiny compared with distances between gas molecules

4. There is little attraction between molecules of a gas

Chapter 6 3

5. Molecules collide with each other, with energy being conserved in the collision

6. Temperature (T) is a measure of the average kinetic energy of the gas molecules

Chapter 6 4

Pressure and Temperature (cont.)

Chapter 6 5

Volume Relationships• Law of combining volumes – when all

measurements are made at same temperature and pressure, volumes of gaseous reactants and products are in small whole-number ratio

Chapter 6 6

• Avogadro’s hypothesis – equal volumes of gases at constant pressure and temperature have the same number of molecules

Chapter 6 7

UNITS

• Pressure

• Temperature

Chapter 6 8

Molar Volume• Volume occupied by 1 mol of gas

• Standard temperature and pressure (STP)– 1 atm pressure and 0°C– 1 mole of gas has volume of 22.4 L

Chapter 6 9

Talk about Density

• This is at STP

Chapter 6 10

Boyle’s Law• PV=PV

Chapter 6 11

Talk about Lungs

A gas is enclosed in a cylinder fitted with a piston. The volume of the gas is 2.00 L at 0.524 atm. The piston is moved to increase the gas pressure to 5.15 atm. Which of the following is a reasonable value for the volume of the gas at the greater pressure?

0.20 L 0.40 L 1.00 L 16.0 L

A gas is enclosed in a 10.2-L tank at 1208 mmHg. (The mmHg is a pressure unit; 760 mmHg = 1 atm.) Which of the following is a reasonable value for the pressure when the gas is transferred to a 30.0-L tank?

300 mmHg 400 mmHg 3,600 mmHg12,000 mmHg

Exercise

EXAMPLE Boyle's Law: Pressure-Volume Relationships

A cylinder of oxygen has a volume of 2.25 L. The pressure of the gas is 1470 pounds per square inch (psi) at 20 °C. What volume will the oxygen occupy at standard atmospheric pressure (14.7 psi) assuming no temperature change?

EXAMPLE Boyle’s Law: Pressure-Volume Relationships

Chapter 6 14

EXAMPLE Boyle’s Law: Pressure-Volume Relationshipscontinued

A sample of air occupies 73.3 mL at 98.7 atm and 0 ºC. What volume will the air occupy at 4.02 atm and 0 ºC?

Exercise 2

A sample of helium occupies 535 mL at 988 mmHg and 25 °C. If the sample is transferred to a 1.05-L flask at 25 °C, what will be the gas pressure in the flask?

Exercise 3

Chapter 6 15

Charles’s Law

Chapter 6 16

Charles' Law• V/T = V/T

A balloon indoors, where the temperature is 27 °C, has a volume of 2.00 L. What would its volume be (a) in a hot room where the temperature is 47 °C, and (b) outdoors, where the temperature is –23 ºC? (Assume no change in pressure in either case.)

EXAMPLE 6.15 Charles’s Law: Temperature-Volume Relationships

Chapter 6 18

a. A sample of oxygen gas occupies a volume of 2.10 L at 25 °C. What volume will this sample occupy at 150 °C? (Assume no change in pressure.)

b. A sample of hydrogen occupies 692 L at 602 °C. If the pressure is held constant, what volume will the gas occupy after being cooled to 23 °C?

Exercise 6.15A

At what Celsius temperature will the initial volume of oxygen in Exercise 6.15A occupy 0.750 L? (Assume no change in pressure.)

Exercise 6.15B

EXAMPLE 6.15Charles’s Law: Temperature-Volume Relationships continued

Chapter 6 19

Ideal Gas Law

PV = nRT

• P = pressure

• V = volume

• n = number of moles

• R = gas constant = 0.0821 L atm/mol K

• T = absolute temperature

EXAMPLE 6.16 Ideal Gas Law

Use the ideal gas law to calculate (a) the volume occupied by 2.00 mol of nitrogen gas at 244 K and .9500 atm pressure, and (b) the pressure exerted by 0.500 mol of oxygen in a 15.0-L container at 303 K.

Determine (a) the pressure exerted by 0.0330 mol of oxygen in an 18.0-L container at 313 K, and (b) the volume occupied by 0.200 mol of nitrogen gas at 298 K and 0.980 atm.

Exercise 6.16A

Chapter 6 21

Determine the volume of nitrogen gas produced from the decomposition of 130 g sodium azide (about the amount in a typical automobile airbag) at 25 °C and 1 atm.

Exercise 6.16B

EXAMPLE 6.16 Ideal Gas Law continued