1. Chapter 10: Physical Characteristics of Gases

2. The Kinetic Molecular Theory (KMT)
describes the behavior of an “ideal” gas.
Ideal gases include the noble gases and diatomic gases
Real gases deviate slightly from the KMT. At high pressures and low temperatures, deviation may be significant because particles begin to condense into liquid.

3. KMT Postulates:
1. Gases consist of tiny particles that are very far apart.
2. Gas particles are in constant straight-line motion.
3. The rate of motion of a gas depends on temperature.
4. Collisions between particles and between particles and container walls are elastic (no loss of energy)
5. Attractive and Repulsive forces do not exist between molecules.

4. Characteristics of Gases
1. Expansion and Compressibility
gases fill containers of any size
2. Low Density
small number of particles in a given space
3. Fluidity
particles slide past each other
4. Ability to Diffuse and Effuse
diffusion –able to spread out and mix with other gases
effusion –able to fit through narrow openings

5. Volume (V) Describing Gases measured in mL or L. (cm3 or dm3)
amount of space occupied by a gas at a specific temperature and pressure.
measured in mL or L. (cm3 or dm3)
1000 mL = 1 L or cm3 = 1 dm3

6. Temperature (T)
Average kinetic energy of particles
Measured in Kelvin
K = °C + 273
Pressure (P)
Force exerted over a given area
Measured in atm, kPa, mmHg (torr)
1 atm = kPa = 760 mmHg (torr)

7. Standard Temperature and Pressure
Special Condition:
Standard Temperature and Pressure
“STP”
0 °C and atm
(273 K) ( kPa)
(760 mmHg)

8. Examples for Converting Units:
275 mL = ? L L = ? mL
35 C = ? K K = ? C
1.15 atm = ? mmHg torr = ? kPa

9. The Gas Laws Boyle’s Law P1V1 = P2V2 animation
Pressure and Volume of a gas are inversely proportional.
Temperature of gas must remain constant.

10. Charles’ Law V1 = V2 T1 T2 animation
Temperature and Volume of a gas are directly proportional.
Pressure of gas must remain constant.
Temperature MUST be measured in Kelvin.

11. Gay-Lussac’s Law P1 = P2 T1 T2
Temperature and Pressure of a gas are directly proportional.
Volume of gas must remain constant.
Temperature MUST be measured in Kelvin.

12. Combines 1st three gas laws into one equation.
Combined Gas Law
P1V1 = P2V2
T T2
Combines 1st three gas laws into one equation.
Temperature MUST be measured in Kelvin.

13. Dalton’s Law of Partial Pressures Pmixture = PA + PB + PC + …
The total pressure of a mixture of gases is equal to the sum of the partial pressures of each gas in the mixture.
Pbar = Pgas + PH2O
For gases that are collected by water displacement, the sum of the partial pressure of the gas and the vapor pressure of water is equal to barometric pressure.

15. Gas Law Problem-Solving Examples:
1. A sample of O2(g) has a volume of 150. mL when its pressure is atm. What will the volume be when the pressure is increased to atm?
2. A sample of Ne(g) has a volume of 752 mL at 25°C. At what Temperature will the volume be 900.mL?

16. 3. A sample of Cl2(g) has a pressure of 100. 5 kPa at 30°C
3. A sample of Cl2(g) has a pressure of kPa at 30°C. At what temperature will the gas be at standard pressure?
4. A gas occupies 1.8 L at 300. K and 738 torr. What will be the volume when the temperature is 325 K and pressure is torr?

17. 5. The pressure of a mixture of gases is measured as 2. 58 atm
5. The pressure of a mixture of gases is measured as atm. If the mixture is composed of gas A (1.21 atm) and gas B (0.96 atm), what is the partial pressure of gas C?
6. A gas is collected over water with barometric pressure measuring atm. The vapor pressure of the water is mmHg. What is the pressure of the gas collected, in mmHg?