1. The Gas Laws
Chapter 14

2. The Kinetic Molecular Theory
Gas particles do not attract or repel each other
Gas particles are very small with large amounts of space between them
Gas particles are in constant random motion
Gas particles have elastic collisions – no energy lost
Gas particles have the same average kinetic energy at the same temperature

3. Gas Pressure
Gas particles exert pressure when they collide with the walls of their containers
Temperature, volume, and the number of moles affect the pressure that a gas exerts
Pressure Units
SI unit for pressure – Pascal (Pa)
101.3 kPa = 1 atm
760 mm Hg = 1 atm
760 torr = 1 atm

4. Gas Laws
4 factors that affect gases – when one changes it changes the other factors
Volume
Temperature
Pressure
Moles (# of particles)

5. Boyle’s Law
As the volume of a container of gas decreases, then the pressure of that gas increases
This is an inverse relationship (as one goes up the other goes down)
Temperature remains constant
P1V1 = P2V2

8. Boyle’s Law – Sample Problem
P1V1 = P2V2
P1 = 1.2 atm check to make sure your
P2 = x your units are the same
V1 = 3.5 L
V2 = 6.4 L
(1.2)(3.5) = P2(6.4)
= P atm = P2

9. Boyle’s Law – Sample Problem
P1V1 = P2V2
P1 = 7.5 atm check to make sure your
P2 = 10.3 atm your units are the same
V1 = x
V2 = 2.65 L
(7.5)V1 = (10.3)(2.65)
= V L = V1

10. Boyle’s Law
Homework – pg # 1-5

11. Charles’ Law
As the temperature of a gas increases so does its volume
This is a direct relationship (the both change in the same direction)
Pressure remains constant =
Temperature must be in Kelvin
K = Celsius + 273

13. Charles’ Law – Sample Problem
V1 = 3.4 L check to make sure your
V2 = 7.8 L your units are the same
T1 = 45°C ( = 318)
T2 = x
= cross multiply
= T K = T2
729 – 273 = 456°C
460°C

14. Gay Lussac’s Law
As the pressure of a gas increases so does its temperature
This is a direct relationship (the both change in the same direction)
Volume remains constant =
Temperature must be in Kelvin

15. Gay Lussac’s Law – Sample Problem
P1 = 4.52 atm check to make sure your
P2 = x your units are the same
T1 = 22°C ( = 295)
T2 = 315 K
= cross multiply
= P atm = P2

16. Charles’ and Gay Lussac’s Law
Homework pg. 425 # 6-8
pg. 427 # 9-13

17. Combined Gas Law Combines pressure, volume, and temperature
Amount of gas (moles) is constant

18. Combined Gas Law - Example
A sample of nitrogen monoxide has a volume of 72.6 mL at a temperature of 16°C and a pressure of kPa. What volume will the sample occupy at 24°C and 99.3 kPa?
P1 = kPa T1 = 16°C
P2 = kPa T2 = 24°C
V1 = 72.6 ml
V2 = X

19. Combined Gas Law - Example
First convert your temperature to Kelvin
T1 = = 289 K
T2 = = 297 K =
(104.1)(72.6)(297) = (289)(99.3)V2
78.2ml = V2
= V2

20. Combined Gas Law - Example
P1 = 98.0 kPa T1 = 25°C = 298
P2 = x T2 = 60°C = 333
V1 = 1.5 L
V2 = L =
= P2
51.3 kPa = P2

21. Combined Gas Law - Homework
Practice problems # pg. 430

22. Ideal Gas Law Particles take up no space
Particles have no intermolecular attractive forces
NO GAS IS TRULY IDEAL!
PV = nRT
P = pressure , V = volume, T = temperature
n = number of moles
R = ideal gas constant (depends on units of
pressure)

23. Ideal Gas Law Volume = Liter Temp = Kelvin n = moles
The value of R depends on the pressure units:
Value of R
Units of Pressure
0.0821
atm
8.314
kPa
62.4
mm Hg ; torr
Volume = Liter
Temp = Kelvin
n = moles

24. Ideal Gas Law – Example = n 0.30mol = n P = 2.5 atm V = 3.2 L
T = 47 °C = 320 K
PV = nRT
Which R value do you use? atm =
(2.5)(3.2) = n (0.0821)(320)
= n
0.30mol = n

25. Ideal Gas Law - Example = 6.06 g n = 0.30 mol
If the molar mass of this gas is 20.2 g/mol. How many grams of this gas do you have?
What is this gas?
0.30 mol x
= 6.06 g
If the molar mass is 20.2 g/mol then the gas is:
Neon

26. Ideal Gas Law – Example 0.61 mol = n = n P = 652 mm Hg V = 17.5 L
T = 27 °C = 300 K
PV = nRT
Which R value do you use?
62.4
(652)(17.5) = n (62.4)(300)
0.61 mol = n
= n

27. Ideal Gas Law – Homework
Practice problems # pg. 437