1. Chapter 12
The behavior of gases

2. 12.1 The properties of gases
Kinetic theory:
1. A gas is composed of particles that are considered to be small, hard spheres. These spheres have insignificant volume and are far apart from one another
2. The particles in a gas move rapidly in constant random motion
3. All collisions are perfectly elastic
Total kinetic energy remains constant

3. Compressibility: a measure of how much the volume of matter decreases under pressure
It is assumed that no attractive forces exist between gas particles. WHY????
Gas particles are moving too rapidly with too much kinetic energy. Collisions are COMPLETELY ELASTIC!

4. Variables that describe a gas
1. Pressure (P): units = pascals or kilopascals
2. Volume (V): units = liters
3. Temperature (T): units = kelvins
4. number of moles (n): unit = moles
Why is temperature in kelvin????

5. Let’s review! Pg
Pg , 26, 47, 48, 49, 50, 75, 77, 78, 79, 81, 82,

6. 12-2 Factors affecting Gas Pressure
Why does a balloon pop?
Think of some ways that you could make a balloon pop.
Sketch what is happening at the molecular level when a balloon pops

7. How can you make a balloon pop?
1. Add more gas
If you increase the number of particles, the number of collisions increase = increase in pressure
2. Decrease the volume (squish it)
The more a gas in compressed, the greater the pressure it exerts inside of the container
3.Raise the Temperature!
Since temperature is a measure of kinetic energy, raising the temperature means a rise in kinetic energy = rise in number of collisions = higher pressure

8. SOOOOOO Number of moles of gas go up? Pressure goes up
Volume goes down? Pressure goes up
Temperature goes up? Pressure goes up
# mole to pressure = direct relationship
Volume to pressure = inverse relationship
Temperature to pressure = direct relationship

9. 12.3 THE GAS LAWS!!! Pressure to Volume = BOYLE’S LAW
we already know that as volume goes down, pressure goes up. This is an inverse relationship (think opposite)
Boyle’s law: for a given mass of a gas at constant temperature, the volume of the gas varies inversely with the pressure
VOLUME GOES UP, PRESSURE GOES DOWN

10. Boyle’s Law Equation
Why constant temperature? Why constant number of moles?
So only one variable is considered at a time.
P1 x V1 = P2 x V2
Since temperature is a constant, and number of moles is a constant, we can look at just temperature and pressure.
Just identify the variables you know and solve for the unknown!

11. Let’s Try it!
1. A high altitude balloon contains 30.0 L of helium gas at 103 kPa. What is the volume when the balloon rises to a pressure that is only 25.0 kPa. Assume that temperature remains a constant.
What do you know?
V1 = 30.0 L, P1 = 103 kPa, P2 = 25.0 kPa
What do you want to know?
The ending volume, V2
Boyle’s law states = P1 x V1 = P2 x V2
Fill in the knowns and solve for the unknown!

12. More Practice!
The pressure on 2.50 L of anesthetic gas changes from 105 kPa to 40.5 kPa. What will be the new volume if temperature remains constant?
1.What do you know?
2. What do you want to know?
3. Plug it into the equation and solve!

13. A gas with a volume of 4.00 L at a pressure of 205 kPa is allowed to expand to a volume of 12.0 L. What is the pressure in the container f the temperature remains constant?

14. Review Boyle’s law= relates volume and pressure P1 x V1 = P2 x V2
Pressure goes up? Volume goes down
Units: volume is generally liters (L), pressure is generally kilopascals (kPa) or atmospheres (atm)
Why do temperature and number of moles have to be constant????

15. You try it!
1. If a gas at 25.0 °C occupies 3.60 liters at a pressure of 1.00 atm, what will be its volume at a pressure of 2.50 atm?
2. A gas occupies 1.56 L at 1.00 atm. What will be the volume of this gas if the pressure becomes 3.00 atm?
3. A gas occupies 11.2 liters at atm. What is the pressure if the volume becomes 15.0 L?
4. A gas occupies 4.31 liters at a pressure of atm. Determine the volume if the pressure is increased to 1.25 atm.
mL of a gas is at a pressure of 8.00 atm. What is the volume of the gas at standard pressure (STP)?

16. Challenge!
6. Chlorine gas occupies a volume of 1.2 liters at 720 torr pressure. What volume will it occupy at 1.0 atm pressure?
7. Fluorine gas exerts a pressure of 200 kPa. When the pressure is changed to 1.50 atm, its volume is 250 mL. What was the original volume?
8. A sample of gas has a volume of 12.0 L and a pressure of 1.00 atm. If the pressure of gas is increased to 1000 mm Hg, what is the new volume of the gas?
9. A container of oxygen has a volume of 30.0 mL and a pressure of 500,000 Pa. If the pressure of the oxygen gas is reduced to 28 psi and the temperature is kept constant, what is the new volume of the oxygen gas?
10. Ammonia gas occupies a volume of 450. mL at a pressure of 720. atm. What volume will it occupy at standard pressure (STP)?
11. A 40.0 L tank of ammonia has a pressure of 1000 mmHg. Calculate the volume of the ammonia if its pressure is changed to 500 torr while its temperature remains constant.
Pressure Conversions:
1 atm = kPa = 101,325 Pa = 760 mm Hg = 760 torr = 14.7 lb/in2 (psi)

17. Charles’ Law Charles’ law relates temperature and volume.
The volume of a fixed mass of gas is directly proportional to it’s kelvin temperature if pressure is kept the same.
Temperature goes up? Volume goes up!
Think of a helium balloon. What happens if you leave it in your trunk over night?
V1/T1 = V2/T2

18. Let’s try it!
A balloon inflated in a room 24 degrees Celsius has a volume of 4.00 L. The balloon is heated to 58 degrees Celsius. What is the new volume if pressure remains constant?
V1= 4.00 L
T1= 24 degrees Celsius
V2= ?
T2= 58 degrees Celsius
V1/T1 = V2/T2
4.00L/ 24 degrees C = ?/ 58 degrees C

19. You try it!
1. If a sample of gas occupies 6.80 L at 325 degrees Celsius, what will be its volume at 25 degrees Celsius if the pressure does not change?
2. Exactly 5.00L of air at degrees Celsius is warmed to degrees Celsius. What is the new volume if pressure remains constant?

20. Gay-Lussac’s Law This law relates temperature and pressure
Gay-Lussac’s law states that the pressure of a gas is directly proportional to the kelvin temperature scale.
Temperature goes up? Pressure goes up!
P1/T1 = P2/T2
YOU MUST CONVER TO KELVIN!!!
K = C + 273

21. Let’s try it!
The Gas left in a used aerosol can is at a pressure of 103 kPa at 25 degrees Celsius. If this can is thrown into a fire, what is the pressure when its temperature reaches 928 degrees Celsius?
Hint: CONVERT TO KELVIN FIRST!!!!
P1= 103 kPa
T1= ( ) = 298 K
P2= ?
T2= ( ) = 1201 K
P1/T1 = P2/T2
103 kPa/ 298 K = ?/1201 K
P2= 415 kPa

22. You Try It!
The pressure in a car tire is 198 kPa at 27 degrees Celsius. At the end of a trip on a hot sunny day, the pressure has risen to 225 kPa. What is the temperature of the air in the tire? Assume that the volume has not changed.
Why do you need to check your tire’s air pressure when it gets cold?

23. (P1 x V1)/T1 = (P2 x V2)/T2 The Combined Gas Law
We can express all of these relationships in a single equation!
(P1 x V1)/T1 = (P2 x V2)/T2

24. Let’s Try It!
The volume of a gas-filled balloon is 30.0L at 40 degrees Celsius and 153 kPa pressure. What volume will the balloon have at STP?
STP = 273 K and kPa
V1= 30.0 L
T1= ( ) 313 K
P1= 153 kPa
V2= ?
T2= 273 K
P2= kPa

25. You Try It!
A gas at 155 kPa and 25 degrees Celsius occupies a container with an initial volume of 1.00L. By changing the volume, the pressure of the gas increases to 605 kPa as the temperature is raised to 125 degrees Celsius. What is the new volume? HINT: CONVERT TO KELVIN!

26. And another one!
A 5.00 L air sample at a temperature of -50 degrees Celsius has a pressure of 107 kPa. What will be the new pressure if the temperature is raised to 102 degrees Celsius and the volume expands to 7.00 L?
HINT: CONVERT TO KELVIN!!!!

27. Your Assignment! Due by end of class 1. Get a laptop
2. Go to my webpage
3. Go to Chem 1B
4. Complete ‘Gas Laws Homework’ on a SEPARATE SHEET OF PAPER!!!
5. SHOW ALL WORK AND THE EQUATIONS NEEDED!!!!
Turn in when finished