1. Chapter 14
Gas
Behavior

2. Kinetic Molecular Theory
Chpt 13 pgs
Particles in a gas are considered to be small, hard spheres with insignificant volume.
The motion of the particles in a gas is rapid, constant, and random.
All collisions between particles in a gas are perfectly elastic.
The Kelvin temperature of a substance is directly proportional to the average kinetic energy of the particles of the substance.

3. COMPRESSIBILITY According to KMT, the particles of a gas are
very far apart. Between the gas particles, there
is mostly empty space.
For this reason, gases are COMPRESSIBLE.
According to KMT, the particles of a gas move in
a constant, random, straight-line motion until they
collide with something. When they collide with the
walls of the container, PRESSURE results.

4. kPa, atm, mm Hg, torr, bar, or psi.
Pressure is defined as the force exerted over a given area.
Pressure can be measured in….
kPa, atm, mm Hg, torr, bar, or psi.
Standard pressure at sea level
101.3 kPa = 1 atm = 760 mm Hg

5. VARIABLES used to describe GASES
1. Amount of gas measured in moles
(variable used ‘n’).
2. Volume of the gas measured in liters
(variable used ‘V’).
3. Temperature of the gas measured in Kelvin
(variable used ‘T’).
4. Pressure of the gas measured in atm or kPa
(variable used ‘P’).

6. How does ‘amount of particles’ affect pressure?
If the number of particles is doubled,
how is the pressure affected?
If the number of particles is tripled,
how is the pressure affected?

7. How does an
aerosol can work?
What happens if you
do not hold the can
upright?
What happens when
the pressure of the
propellant equals the
air pressure outside
the can?

8. What happens to the gas pressure when the
volume of the container is reduced by one-half?

9. What happens to the pressure of a gas when the
temperature of the gas is doubled?
What eventually happens if the temperature
continues to increase?

10. The Gas Laws
Section 14.2

11. P1 V1 T1 P2 V2 T2 = Combined Gas Law
Describes the relationship among pressure,
temperature, and volume of an enclosed gas
when the amount of gas is the only variable
held constant.
P1 V1 T1
P2 V2 T2 =

12. If n is held constant, there is a direct
relationship between PV and T.
P x V T

13. Example: A gas at 155 kPa and 25oC has an
initial volume of 1.00 L. The pressure of the
gas increases to 605 kPa as the temperature
is raised to 125oC. What is the new volume?
0.342 L
Example: A 5.00 L air sample has a pressure of
107 KPa at a temperature of -50.0oC. If the
temperature is raised to 102oC and the volume
expands to 7.00 L, what will the new pressure be?
129 kPa

14. P1V1 = P2V2 T2 T1 Boyle’s Law If T and n remain the same,
P increases as V decreases.
P1V1 = P2V2 T1 T2
Pressure and Volume are inversely proportional.

15. The ‘curve’ shows an inverse relationship.

16. Example: Nitrous oxide (N2O) is used as an
anesthetic. The pressure on 2.50 L of N2O
changes from 105 kPa to 40.5 kPa. If the
temperature does not change, what will the
new volume be?
6.48 L
Example: A gas with a volume of 4.00 L at a
pressure of 205 kPa is allowed to expand to
a volume of 12.0 L. What is the pressure in
the container if the temperature remains
constant?
68.3 kPa

17. P1V1 P2V2 T1 T2 Charles’s Law If P and n remain the same,
V increases as T increases.
P1V1 T1
P2V2 T2 =
Volume and temperature
are directly proportional.

18. Example illustrating Charles’s Law

19. Direct relationship between volume and temperature

20. Example: If a sample of gas occupies 6.80 L
at 325oC, what will its volume be at 25oC if
the pressure does not change?
3.39 L
Example: Exactly 5.00 L of air at -50.0oC is
warmed to 100.0oC. What is the new volume
if the pressure remains constant?
8.36 L

21. P1V1 T1 P2V2 T2 = Gay-Lussac’s Law If V and n remain the same,
T increases as P increases.
P1V1 T1
P2V2 T2 =
Pressure and Temperature
are directly proportional.

22. If the temperature in the container is doubled,
what happens to the pressure?

23. Example: A sample of nitrogen gas has a pressure
of 6.58 kPa at 539 K. If the volume does not
change, what will the pressure be at 211 K?
2.58 kPa
Example: The pressure in a car tire is 198 kPa at
27oC. After a long drive, the pressure is 225 kPa.
What is the temperature of the air in the tire?
Assume that the volume is constant.
341 K or 68oC.

24. Ideal Gas Law

25. “universal gas constant”
Ideal Gas Law
PV = nRT
“R” is called the
“universal gas constant”

26. Volume of 1 mole of gas at STP
Standard Temperature
and Pressure
(STP)
Temperature 0oC or 273K
Pressure 1 atm
Volume of 1 mole of gas at STP
22.4L

27. Calculating the value of R
At STP, 1 mole of a gas has a
volume of 22.4L, a temperature
of 273K and a pressure of 1 atm.

28. Using the ideal gas law:PV nT
1.00 atm x 22.4 L
1.00 mol x 273K
R = =
L atm
mol K =

29. Variations of R
kPa L
mol K
R =
atm L
mol K
R =

30. What is the volume (in L)
of 2.5 moles of oxygen gas
measured at 25oC and a
pressure of 104.5kPa?
Answer: 59 L

31. At what temperature will
mole of argon gas
have a volume of 275 mL
at a pressure of kPa?
Answer: 331 K

32. The Ideal Gas Law
and
Stoichiometry

33. What volume of carbon dioxide
forms at 10oC and 99 kPa pressure
when 0.50 g of sodium
bicarbonate reacts completely
with hydrochloric acid?
Answer: L

34. Magnesium is one metal that
is able to react with nitrogen
directly. What volume of
nitrogen, measured at a pressure
of 102 kPa and a temperature of
27oC, will react with 5.0 g of
magnesium?
Answer: 1.7 L

35. Section 14.4
Gases:
Mixtures
and
Movement

36. Dalton’s Law of
Partial Pressure
Partial Pressure - In a
mixture of gases, the
individual pressure of
each gas.

37. Dalton’s Law of
Partial Pressure
The total pressure of a mixture
of gases is the sum of the partial
pressures of the individual gases
in the mixture.

38. Dalton’s Law of
Partial Pressure
In equation form:
Ptotal = Pa + Pb + Pc + ...

39. You collect a sample of
oxygen gas by the water-
displacement method. If the
atmospheric pressure is
99.4 kPa and the water-vapor
pressure is 4.5 kPa, then what
is the partial pressure of the
oxygen gas?

40. Use Dalton’s Law of Partial
Pressures:
Ptotal = Pa + Pb
Ptotal = Pwater-vapor + Poxygen gas
99.4 kPa = 4.5 kPa + Poxygen gas
Poxygen gas = 94.9 kPa

41. the tendency of molecules to move toward areas of lower concentration
Diffusion
the tendency of molecules to move
toward areas of lower concentration
until the concentration is uniform throughout.
Effusion
when a gas escapes through a tiny
hole in its container.
Graham’s Law
The rate of effusion of a gas is
inversely proportional to the
square root of the gas’s molar mass.

42. Compare the rates of effusion
= √
Rate A
Rate B
Molar Mass B
Molar Mass A
Example:
Compare the rates of effusion
for helium and argon.

43. Compare the rates of effusion
Example:
Compare the rates of effusion
for oxygen and radon.