1. Unit 8 Chemistry Langley
BEHAVIOR OF GASES
Unit 8
Chemistry
Langley
**Corresponds to Chapter 14 in the Prentice Hall Chemistry Book

2. PROPERTIES OF GASES No definite shape/volume
Expands to fill its container
Easily compressed (squeezed into a smaller container)
Compressibility is 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. PROPERTIES OF A GAS Factors Affecting Gas Pressure
Amount of Gas
Increase amount, increase pressure
Volume
Reduce volume, increase pressure
Temperature
Increase temperature, increase pressure
Relationship between pressure, temperature, and volume is explained through the Gas Laws

4. GAS LAWS Boyle’s Law Charles’ Law Gay-Lussac’s Law Combined Gas Law
Ideal Gas Law
Dalton’s Law of Partial Pressure
Graham’s Law

5. BOYLE’S LAW
If the temperature is constant, as the pressure of a gas increases, the volume decreases
For a given mass of gas at constant temperature, the volume of a gas varies inversely with pressure
As volume goes up, pressure goes down
As volume goes down, pressure goes up
P1V1 = P2V2

6. BOYLE’S LAW Real Life Example Mathematical Example 1:
As you push on the end of a syringe, the volume inside the syringe decreases as the pressure on the syringe increases
Mathematical Example 1:
P1 = 758 torr V1 = 5.0L P2 = ? V2 = 3.5L

7. BOYLE’S LAW Mathematical Example 2
If 4.41 dm3 of nitrogen gas are collected at a pressure of 94.2 kPa, what will the volume be for this gas at standard pressure if the temperature does not change?

8. CHARLES’ LAW
As the temperature of an enclosed gas increases, the volume increases, if the pressure is constant
The volume of a fixed mass of gas is directly proportional to its Kelvin temperature if the pressure is kept constant
As volume goes up/down, temperature goes up/down
V1 = V Temperature must be in Kelvin! T T2

9. CHARLES’ LAW Real Life Example
Balloon Lab-As the temperature of the water is increased, the volume of the balloon is increased.
Coke Can-Fill a coke can with a small amount of water, as you heat the water inside to near boiling, immediately invert the coke can into ice-cold water so the coke can is experiencing a dramatic drop in temperature, volume of can will decrease (can will crush in on itself)

10. CHARLES’ LAW Mathematical Example 1 Mathematical Example 2
V1 = 250mL T1 = 300K V2 = 321mL T2 = ?
Mathematical Example 2
With a constant pressure, the volume of a gas is increased from 15.0L to 32.0L. If the new temperature is 20.0°C, what was the original temperature?

11. GAY-LUSSAC’S LAW
As the temperature of an enclosed gas increases, the pressure increases, if the volume is constant
The pressure of a gas is directly proportional to the Kelvin temperature if the volume remains constant
P1 = P Temperature must be in Kelvin! T1 T2

12. GAY-LUSSAC’S LAW Real Life Example Mathematical Example 1 Tires
The faster a car goes, the higher the temperature of the tire gets and the higher the pressure inside the tires
Mathematical Example 1
P1 = ? T1 = 456K P2 = 789mmHg T2 = 326K

13. GAY-LUSSAC’S LAW Mathematical Example 2
The pressure in a tire is 1.8 atm at 20°C. After a 200 mile trip, the pressure reading for the tire is 1.9 atm. What is the temperature inside the tire at that new pressure?

14. COMBINED GAS LAW Combines Boyle’s, Charles’, and Gay-Lussac’s laws
Describes the relationship among temperature, pressure, and volume of an enclosed gas
Allows you to perform calculation for situations IF and ONLY IF the amount of gas is constant
P1V1 = P2V Temperature must be in Kelvin!
T T2

15. IDEAL GAS LAW
When you need to account for the number of moles of gas in addition to pressure, temperature, and volume, you will use the Ideal Gas Equation
Modified version of the Combined Gas Law
PV = nRT
n = number of moles
R = ideal gas constant
(L-atm/mol-K)
62.4 (L-mmHg/mol-K)
8.314 (L-kPa/mol-K)

16. IDEAL GAS LAW Mathematical Example 1 Mathematical Example 2
What is the pressure in atm exerted by 0.5 moles of N2 in a 10L container at 298 Kelvin?
Mathematical Example 2
What is the volume in liters of moles of O2 at 20°C and atm?

17. IDEAL GAS LAW Mathematical Example 3 Mathematical Example 4
What is the temperature of 76 grams of Cl2 in a 24L container at 890mmHg?
Mathematical Example 4
A deep underground cavern contains 2.24x106L of CH4 at a pressure of 1.50x103kPa and a temperature of 315K. How many kilograms of CH4 does the cavern contain?

18. IDEAL vs. REAL GASES
Ideal gases follow the gas laws at all conditions of pressure and temperature
Conforms exactly to the all the assumptions of the kinetic theory (no volume, no particle attraction)doesn’t exist
Real gases differ mostly from an ideal gas at low temperature and high pressure
Under other conditions, behave as an ideal gas would

19. DALTON’S LAW
In a mixture of gases, the total pressure is the sum of the partial pressure of the gases
Partial pressure is the contribution each gas in a mixture makes to the total pressure
At constant volume and temperature, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the component of gases
Ptotal = P1 + P2 + P3 + …

20. DALTON’S LAW Mathematical Example 1
In a container there are 4 gases with the following pressures: Gas atm, Gas atm, Gas mmHg, Gas atm; find the total pressure in the container.

21. DALTON’S LAW Mathematical Example 2
In a sample of HCl gas, the pressure of the gas is found to be 0.87 atm. If hydrogen makes up 34% of the gas, what is the pressure of the hydrogen?

22. GRAHAM’S LAW
The ratio of the speeds of two gases at the same temperature is equal to the square root of the inverted molar masses
The relative rate of diffusion
Diffusion is the tendency of molecules to move toward areas of lower concentration to areas of higher concentration until the concentration is uniform throughout
Gases of lower molar mass diffuse and effuse faster than gases of higher molar mass
Effusion is when gas particles escape through tiny holes in a container

23. GRAHAM’S LAW √(Molar MassB/Molar MassA)
The rates of effusion of two gases are inversely proportional to the square roots of their molar masses
Use periodic table to get molar masses

24. GRAHAM’S LAW Mathematical Example 1 Mathematical Example 2
What is the ratio of the speeds of Helium compared to Oxygen?
Mathematical Example 2
If Co2 has a speed of 22 m/s at 20°C, what is the speed of HCl at the same temperature?