1. GASES
Chapter 14

2. From last chapter… Kinetic Molecular Theory
Particles in an ideal gas…
have no volume.
have elastic collisions.
are in constant, random, straight-line motion.
don’t attract or repel each other.
have an avg. KE directly related to Kelvin temperature.

3. Real Gases Particles in a REAL gas… Gas behavior is most ideal…
have their own volume
attract each other
Gas behavior is most ideal…
at low pressures
at high temperatures
in nonpolar atoms/molecules

4. Properties of Gases
Compressibility – gases are easily compressed because of the space between the particles in a gas
Gases expand to take the shape and volume of their container

5. Factors Affecting Gas Pressure
Amount of gas – more particles have more collisions with the container walls and thus create more pressure
Volume – if you reduce the volume of the container, the particles are more compressed and exert a greater pressure on the walls of the container
Temperature – increasing temperature increases the kinetic energy of the particles, which then strike the walls of the container with more energy

6. Remember? Units of Pressure
KEY UNITS AT SEA LEVEL
kPa (kilopascal)
1 atm
760 mm Hg
760 torr
14.7 psi
*These are all equivalent amounts of pressure

7. Standard Temperature & Pressure
STP
Standard Temperature & Pressure
0°C K
1 atm kPa
-OR-

8. The Gas Laws 14.2 P V T

9. Boyle’s Law
The pressure and volume of a gas are inversely related
at constant mass & temp
P1V1 = P2V2 P V

10. Gas Law Problem BOYLE’S LAW P V
A gas occupies 100. mL at 150. kPa. Find its volume at 200. kPa.
BOYLE’S LAW
GIVEN:
V1 = 100. mL
P1 = 150. kPa
V2 = ?
P2 = 200. kPa P V
WORK:

11. Charles’ Law
The volume and absolute temperature (K) of a gas are directly related
at constant mass & pressure V T

12. Gas Law Problem CHARLES’ LAW T V
A gas occupies 473 cm3 at 36°C. Find its volume at 94°C.
CHARLES’ LAW
GIVEN:
V1 = 473 cm3
T1 = 36°C = 309K
V2 = ?
T2 = 94°C = 367K T V
WORK:

13. Gay-Lussac’s Law
The pressure and absolute temperature (K) of a gas are directly related
at constant mass & volume P T

14. Gas Law Problem GAY-LUSSAC’S LAW P T
A gas’ pressure is 765 torr at 23°C. At what temperature will the pressure be torr?
GAY-LUSSAC’S LAW
GIVEN:
P1 = 765 torr
T1 = 23°C = 296K
P2 = 560. torr
T2 = ? P T
WORK:

15. Combined Gas Law
P1V1 T1 =
P2V2 T2

16. Gas Law Problem COMBINED GAS LAW P T V V1 = 7.84 cm3 P1 = 71.8 kPa
A gas occupies 7.84 cm3 at 71.8 kPa & 25°C. Find its volume at STP.
COMBINED GAS LAW
GIVEN:
V1 = 7.84 cm3
P1 = 71.8 kPa
T1 = 25°C = 298 K
V2 = ?
P2 = kPa
T2 = 273 K
P T V
WORK:

17. Avogadro’s Law
The volume and number of moles of a gas are directly related
at constant temperature & pressure V n

18. Gas Law Problem AVOGADRO’S LAW n V GIVEN: V1 = 36.7 L n1 = 1.5 mol
Consider two sample of N2 gas. Sample 1 contains 1.5 mol of N2 and has a volume of 36.7 L at 25°C and 1 atm. Sample 2 has a volume of 16.5 L at 25°C and 1 atm. Calculate the number of moles of N2 in Sample 2.
AVOGADRO’S LAW
GIVEN:
V1 = 36.7 L
n1 = 1.5 mol
V2 = 16.5 L
n2 = ? n V
WORK:

19. UNIVERSAL GAS CONSTANT
Ideal Gas Law
PV=nRT
UNIVERSAL GAS CONSTANT
R= Latm/molK
R=8.315 dm3kPa/molK

20. Ideal Gas Law Problem P = ? atm n = 0.412 mol T = 16°C = 289 K
Calculate the pressure in atmospheres of mol of He at 16°C & occupying 3.25 L.
GIVEN:
P = ? atm
n = mol
T = 16°C = 289 K
V = 3.25 L
R = Latm/molK
WORK:

21. 14.4 - Dalton’s Law of Partial Pressures
The partial pressure of a gas is the pressure that the gas would exert if it were alone in the container.
Dalton’s Law of Partial Pressures says that the total pressure of a mixture of gas is equal to the sum of the partial pressures of all gases in the mixture. Or,
Ptotal = P1 + P2 + P3 +…
Note: you can calculate the partial pressures of the gases if they behave ideally using the ideal gas law (P = nRT/V)

22. Dalton’s Law Example
A 2.0 L flask contains a mixture of nitrogen gas and oxygen gas at 25°C. The total pressure of the gaseous mixture is 0.91 atm, and the mixture is known to contain mol of N2. Calculate the partial pressure of oxygen and the moles of oxygen present.

23. Graham’s Law of Effusion
Diffusion is the tendency of molecules to move toward areas of lower concentration until the concentration is uniform throughout
Effusion is when a gas escapes through a tiny hole in its container
Gases of lower molar mass diffuse and effuse faster than gases of higher molar mass

24. Graham’s Law of Effusion
The rate of effusion of a gas is inversely proportional to the square root of the gas’s molar mass.
This equation compares effusion rates for two gases

25. Graham’s Law Problem
Calculate the ratio of the velocity of hydrogen molecules (H2) to the velocity of carbon dioxide (CO2) molecules at the same temperature.

26. Gas Stoichiometry Yes, we are going back to those 3 step problems…
Molar volume of a gas is the volume that is occupied by 1 mol of an ideal gas at STP.
1 mol of gas occupies 22.4 L
Yes, we are going back to those 3 step problems…

27. Gas Stoichiometry Problem
Quicklime, CaO, is produced by heating calcium carbonate. Calculate the volume of carbon dioxide produced at STP from the decomposition of 152 g of calcium carbonate according to the reaction CaCO3 (s)  CaO (s) + CO2 (g)