1. Gas!!!
It’s Everywhere!!!!

2. Kinetic Molecular Theory
Most of the volume occupied by a gas is empty space
Collisions between gas particles are elastic collisions
Energy is transferred between the particles

3. Kinetic Molecular Theory
Gas particles are in constant motion
Possess kinetic energy (energy of motion)
Kinetic Energy in a gas depends on the temperature
KE = ½ mv2

4. Kinetic Molecular Theory
Expansion
No definite shape or volume
Fluidity
Gases flow like liquids
Low Density
Most of the volume is empty space
Compressibility
Since mostly empty space, particles can be squeezed into a smaller volume

5. Diffusion
Spontaneous mixing of gas particles caused by their random motion

6. Effusion
A process by which gas particles pass through a small opening

7. Diffusion vs. Effusion

8. Real vs. Ideal
Ideal Gas – An imaginary gas that perfectly fits all of the assumptions of the Kinetic Molecular Theory
Real Gas – A gas that does not behave completely according to the assumptions of the Kinetic Molecular Theory
A real gas can behave like an ideal gas under high temperature and low pressure conditions

9. STP STP = Standard Temperature and Pressure Standard Temperature = 0°C
Standard Pressure = 1 atm

10. Pressure The force per unit area on a surface
Barometer – a device used to measure atmospheric pressure

11. Units of Pressure Millimeters of mercury – mmHg Torr Atmosphere – atm
Pascal – Pa
Kilopascal - kPa

12. Important Conversion 1 atm = 760 mmHg 1 atm = 760 torr
1 atm = kPa

13. Temperature
Kelvin is the standard temperature scale used when dealing with gases
Absolute zero = 0 K
Unreachable!
Temperature in Kelvin = Temperature in Celsius + 273
Temperature in Celsius = Temperature in Kelvin – 273
0°C = 273 K
25°C = 298 K (Room Temp)
0 K = -273°C (Absolute Zero)

14. Boyle’s Law
The volume of a gas at constant temperature varies indirectly with pressure.

15. Example
The pressure exerted on a 240 mL sample of hydrogen gas at constant temperature is increased from atm to atm. What will the final volume of the sample be?
V1 = mL
V2= ?
P1 = atm
P2 = atm
P1V1 = P2V2
(0.428 atm)(240.0 mL) = (0.724 atm)V2
V2 = 142 mL

16. Charles’ Law
The volume of a gas at constant pressure varies directly with the temperature

17. Example
A sample of air has a volume of mL at 67°C. At what temperature will its volume be 50.0 mL at constant pressure?
V1 = mL
V2= 50.0 mL
T1 = 67°C = 340 K
T2 = ? V1 V2 V2 T1
(50.0 mL)(340K) T2 = =
= 121 K =
140.0 mL T1 T2 V1

18. Gay-Lussac’s Law
The pressure of a gas at constant volume varies directly with the temperature

19. Combined Gas Law

20. Example
A helium filled balloon has a volume of 50.0 L at 25°C and 1.08 atm. What volume will it have at atm and 10°C?

21. Solution Step 1: List what you are given. V1 = 50.0 L V2= ????
P1 = 1.08 atm
P2 = atm
T1 = 25°C = 298 K
T2 = 10°C = 283 K
Must Convert to Kelvin!!!!

22. Solution
Step 2: Solve the Combined Gas Law for your unknown.

23. Solution Step 3: Solve! V2 = V2 = (1.08 atm)(50.0 L)(283 K)
(0.855 atm)(298 K)
V2 =
60.0 L He

24. Dalton’s Law
The total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases.
PT = P1 + P Pn

25. Example
What is the total pressure of a gas containing a mixture of three gases whose partial pressures are 20 kPa, 10 kPa, and 30 kPa?
PT = P1 + P Pn
PT = 20 kPa + 10 kPa + 30 kPa
PT = 60 kPa

26. Ideal Gas Law
The mathematical relationship among pressure, volume, temperature, and the number of moles of a gas.

27. Example
Calculate the volume, in liters, occupied by 2.00 mol of H2 at 300 K and 1.25 atm (R = )
PV = nRT
nRT
V = P
(2.00mol)(0.0821)(300K)
V =
1.25 atm
V = 39.4 L

28. Avogadro’s Law
Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

29. Gas Stoichiometry 2CO + O2 2CO2
How many liters of oxygen are required to produce 2 L of carbon dioxide?
2CO + O2 2CO2
2L CO2
1L O2
= 1L O2
2L CO2