1. The Gaseous State of Matter
Chapter 12
The Gaseous State of Matter

2. 12.1 General Properties Least dense, most mobile of the three states
Move at high velocities
Large kinetic energy
Example – Water
1 mol = liquid state
1 mol = gas state

3. 12.2 The Kinetic-Molecular Theory
Boyle’s theory to explain behavior and properties of gases
Ideal gasses (low P, high T)
Consist of tiny particles
Distance between particles is large, mostly empty space
Particles have no attraction for each other
Particles move in straight lines with frequent collisions with each other and container walls
All collisions are perfectly elastic
The average KE for all particles is the same for all gases at the same T, value is directly proportional to the T in Kelvin

4. 12.2 Cont’d.
KE = ½mv2
Diffusion – 2 or more gases mix spontaneously until they form a uniform mixture
Effusion – process by which gas molecules pass through a small opening (from a container of high P to low P)
Can use density in place of Molar Mass

5. 12.3 Measurement of Pressure of Gases
Pressure – force per unit area
Atmospheric Pressure – pressure exerted by the atmosphere
Barometer – instrument to measure pressure of gases in the atmosphere

6. Practice 12.1
A barometer reads 1.12 atm. Calculate the corresponding pressure in:
Torr
mmHg

7. 12.4 Dependence of Pressure on Number of Molecules and Temperature
Pressure is produced by gas molecules colliding with the walls of a container
Number of collisions is dependent on the number of particles and temperature
Double the number particles, double pressure
Increase T, increase P

8. 12.5 Boyle’s Law
P1V1 = constant T

9. Practice 12.2
A gas occupies a volume of 0.750atm. At what pressure will the volume be 4.86L?

10. 12.6 Charles’ Law
V1/T1 = Constant P (T must be in K)

11. 12.3 Practice
A 4.50L container of nitrogen gas at 28.0*C is heated to 56.0*C. Assuming that the volume of the container can vary, what is the new volume of the gas?

12. 12.7 Gay-Lussac’s Law P1/T1 = P2/T2 @ constant V (T must be in K)
A gas cylinder contains 40.0L of a gas at 45.0*C and has a pressure of 650.torr. What will the pressure be if the temperature is changed to 100*C?

13. 12.8 Combined Gas Law
P1V1 = P2V STP – Standard Temperature and Pressure
T T2 0*C and 1 atm (760 torr or kPa)
15.00L of gas at 45.0*C and 800.torr are heated to 400.*C, and the pressure is changed to 300.torr. What is the new volume?
To what temperature must 5.00L of oxygen at 50.*C and 600.torr be heated in order to have a volume of 10.0L and a pressure of 800.torr?

14. 12.9 Dalton’s Law of Partial Pressures
The total pressure of a mixture of gases is the sum of the partial pressures exerted by each of the gases in the mixture.
Ptotal = P1 + P2 + P3 + …
When a gas is collected over water, the pressure of the gas is found by:
Pgas collected = Patm – PH2O

15. Practice 12.7
Hydrogen gas was collected by downward displacement of water. A volume of 600.0mL of gas was collected at 25.0*C and 740.0torr. What volume will the dry hydrogen gas occupy at STP?

16. 12.10 Avogadro’s Law
From Gay-Lussac’s Law  when measured at the same T and P, the ratios of volumes of reacting gases are small whole numbers, which leads to…
Avogadro’s Law – Equal volumes of different gases at the same T and P contain the same number of molecules

17. 12.10 Cont’d. Important because:
It offered rational explanation of Gay-Lussac’s Law
Provided a method for determining molar masses of gases and for comparing densities of gases of known molar masses
Gave a firm foundation for the KMT

18. 12.11 Mole-Mass-Volume Relationships of Gases
Any mole of a gas will have the same volume as a mole of any other gas at the same temperature and pressure
Molar Volume –
1 mole of gas occupies STP

19. Practice 12.8
A gas with a mass of 86g occupies 5.00L at 25*C and 3.00atm pressure. What is the molar mass of the gas?

20. 12.12 Density of Gases Density = mass/volume = g/L
dSTP = (molar mass)(1mol/22.4L)
Molar mass = (dSTP)/22.4L/1mol)
These problems  basic unit conversion
The molar mass of a gas is 20.g/mol. Calculate the density of the gas at STP.

21. 12.13 Ideal Gas Law PV=nRT R=0.0821 L*atm/mol*K
A 23.8L cylinder contains oxygen gas at 20.0*C and 732torr. How many moles of oxygen are in the cylinder?
A 0.286g sample of a certain gas occupies 50.0mL at standard temperature and 76.0cmHg. Determine the molar mass of the gas.

22. 12.4 Gas Stoichiometry
For reacting gases at constant temperature and pressure, volume-volume relationships are the same mole-mole relationships.

23. Practice 12.13
What volume of oxygen will react with 15.0L of propane (C3H8) to form carbon dioxide and water? What volume of carbon dioxide will be formed? What volume of water will be formed? C3H8(g) + 5 O2(g)  3 CO2(g) + 4 H2O(g)

24. 12.15 Real Gases
Most gases behave according to the gas laws (ideally) over a wide range of temperatures and pressures
When molecules become crowded (high P and/or low T) they deviate from ideal behavior
Become liquids

25. Homework
Required:
2-48 (even)
Suggested:
1-47 (odd)