1. Chapter 14
The Behavior of Gases

2. Properties of Gases
Compressibility – a measure of how much the volume of matter decreases under pressure
Gases are easily compressed because of the space between the particles in a gas

3. Factors Affecting Gas Pressure
1. The amount of gas
2. Volume
3. Temperature

4. 1. Amount of Gas When a gas is pumped into a container:
pressure increases
Number of collisions increase

6. 2. Volume
When volume decreases, pressure increases (inverse relationship)
If volume is doubled, pressure is halved

7. 3. Temperature (Kelvin)
As temperature increases, pressure increases (proportional)
If temperature (Kelvin) is doubled, pressure is doubled

9. Standard Temperature and Pressure (STP)

10. The Gas Laws Boyle’s Law: Pressure and Volume
Charles’s Law: Volume and Temperature
Gay-Lussac’s Law: Pressure and Temperature
The Combined Gas Law

11. Boyle’s Law: Pressure and Volume
As the pressure increases, volume decreases, if temperature is constant
Inverse relationship
Table T
P1 x V1 = P2 x V2

12. Boyle’s Law

13. Graphs based on Boyle’s Law
Volume versus pressure
Figure: 10-07

14. Sample Exercise
A balloon contains 30.0 L of helium gas at 103 kPa. What is the volume of the helium when the balloon rises to an altitude where the pressure is only 25.0 kPa? (temperature remains constant)
Answer: 124 Liters

15. Practice Exercise
Nitrous oxide (N2O) is used as an anesthetic. The pressure on L of N2O changes from 105 kPa to 40.5 kPa. If the temperature does not change, what will the new volume be?
Answer: 6.48 Liters

16. 2. Charles’s Law: Volume and Temperature
As the temperature of an enclosed gas increases, the volume increases, if the pressure is constant
Direct relationship
V = V2
T1 T2

17. Illustration of Charles’s Law
Volume of an enclosed gas as a function of temperature at constant pressure
The dashed line is an extrapolation to temperatures at which the substance is no longer a gas
Figure: 10-09

18. Sample Exercise
A balloon, inflated in an air-conditioned room at 27C, has a volume of 4.0L. The balloon is then heated to a temperature of 57C. What is the new volume of the balloon if the pressure remains constant?
Answer: 4.4 liters

19. Practice Exercise
If a sample of gas occupies 6.8L at 327C, what will its volume be at 27C if the pressure does not change?
Answer: 3.4 Liters

20. Gay-Lussac’s Law: Pressure and Temperature
As the temperature of a gas increases, pressure increases, if volume is constant
Direct relationship
P1 = P2
T1 T2

21. Sample Exercise
A sample of nitrogen gas has a pressure of kPa at 539 K. If the volume does not change, what will the pressure be at 211 K ?
Answer: 2.58 kPa

22. Practice Exercise
The pressure in a car tire is 198 kPa at 27°C. After a long drive, the pressure is 225 kPa. What is the temperature of air in the tire? Assume that the volume is constant.
Answer: 341 Kelvin

23. 4. The Combined Gas Law

24. Sample Exercise
A 5.00 L air sample has a pressure of 107 kPa at a temperature of -50°C. If the temperature is raised to 102°C and the volume expands to 7.00 L, what will the new pressure be?
Answer : 129 kPa

25. Sample Exercise
The volume of a gas filled balloon is 30.0 L and 313 K and 153 kPa pressure. What would the volume be at standard temperature and pressure?
Answer : 39.5 Liters

26. Diffusion – the tendency of molecules to move toward areas of lower concentration until the concentration is uniform throughout
Effusion – a gas escapes through a tiny hole in its container
Gases with a lower molar mass (g/mol) diffuse and effuse faster than a gas with a higher molar mass.

27. Ideal Gases and Real Gases
Particles have no volume
There is no attraction between molecules
Ideal gases do not exist (kind of: H2 and He behave Ideally)
Needs high temperature and low pressure
Real Gases
Have volume
There are attractions between molecules (can condense)
Needs low temperature and high pressure

28. Ideal Gases Calculates the number of moles (n) of a contained gas
PV = nRT
Ideal gas constant (R) = 8.31 𝐿 ·𝑘𝑃𝑎 𝑚𝑜𝑙 ·𝐾

29. Sample Exercise
A deep underground cavern contains 2.24 x 106 L of methane gas (CH4) at a pressure of 1.50 x 103 kPa and a temperature of 315 K. How many kilograms of CH4 does the cavern contain?

30. Practice Problems
A child’s lungs can hold 2.20 L. How many grams of air do her lungs hold at a pressure of 102 kPa and a body temperature of 37°C? Use a molar mass of 29 grams (per mole) for air, which is about 20% O2 (32 g/mol) and 80% N2 (28 g/mol)