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
1
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
2
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
3
Pressure and Temperature
(cont.)
Chapter 6
4
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
5
• Avogadro’s hypothesis – equal volumes
of gases at constant pressure and
temperature have the same number of
molecules
Chapter 6
6
UNITS
• Pressure
• Temperature
Chapter 6
7
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
8
Talk about Density
• This is at STP
Chapter 6
9
Boyle’s Law
• PV=PV
Chapter 6
10
Talk about Lungs
Chapter 6
11
EXAMPLE
Boyle's Law: Pressure-Volume Relationships
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
Exercise
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
12,000 mmHg
400 mmHg 3,600 mmHg
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
continued
Exercise 2
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 3
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?
Chapter 6
14
Charles’s Law
Chapter 6
15
Charles' Law
• V/T = V/T
Chapter 6
16
EXAMPLE 6.15
Charles’s Law: Temperature-Volume
Relationships
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 continued
Exercise 6.15A
a.
b.
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.)
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 6.15B
At what Celsius temperature will the initial volume of oxygen in Exercise
6.15A occupy 0.750 L? (Assume no change in pressure.)
Chapter 6
18
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
Chapter 6
19
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.
Exercise 6.16A
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.
EXAMPLE 6.16
Ideal Gas Law continued
Exercise 6.16B
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.
Chapter 6
21