Pre-University Chemistry

1. 1
The Behavior of
Gases
1. Describe the properties of gas particles
(according to the kinetic theory).
2. Explain how the kinetic energy of gas
particles relates to Kelvin temperature. What
happens to these particles as the average
KE changes?
3. What are some variables/factors that would
impact a gases behavior?

2. 2
Assumptions of the Kinetic Theory
of Gases (Review!)
 1. The volumes of individual gas particles
are very small in relation to the distances
between them. Thus, there is a large
amount of empty space between gas
particles.
 2. There are no attractive or repulsive
forces existing between particles. Thus,
gas particles move about in an independent
fashion, occupying the full volume of their
container.

3. 3
 3. Gas particles tend to be in constant
motion, traveling in straight paths until
chance collisions with other particles or a
wall alters their course.
 4. Collisions between gas particles are
perfectly elastic, that is, kinetic energy is
transferred without loss from one particle
to another.
 5. The average kinetic energy of the gas
particles is directly proportional to Kelvin
temperature.

4. 4
Variables that Describe a Gas
Pressure (P) – kPa, atm or mm Hg
(1 atm = 760 mm Hg = 101.3 kPa)
 Volume (V) – L (liters)
 Temperature (T) – K (Kelvin)
K = 273 + °C
 Number of moles (n)

5. 5
Chapter 11: Gases
 Kinetic Molecular Theory:
particles constantly in
motion
 Avg. KE, temperature,
pressure, volume and
amount of a gas all related

6. 6
Air Pressure & Force
 Air Pressure due to the
collision of molecules
on surfaces
 Pressure = defined as
the force per unit area
on a surface
 Pressure =
 Force unit: newton (N)
Force
Area

7. 7
The Barometer
 Pressure depends on area
of contact; smaller area,
greater pressure
• Atmosphere exerts
pressure - total of individual
gas pressures (mostly N,
then O)
• Measured using
barometers
• Units/values/CF’s
(ie. 1 torr = 1 mmHg)

8. 8
Dalton’s Law of Partial
Pressures
 Partial pressures are
exerted by individual
gases
 Law states that total
pressure of a gas
mixture is the sum of
the component
pressures
 PT = P1+P2+P3…

9. 9
Boyle’s Law
The 5 Gas Laws
There are relationships (direct and indirect) between pressure,
temperature and volume (as well as with the # of moles n.)
The 5 gas laws take all of these relationships into account.
1) Boyle’s Law
2) Charles’s Law
3) Gay-Lussac’s Law (really)
4) The Combined Gas Law
5) The Ideal Gas Law

10. 10
Boyle’s Law
Inversely relates pressure and volume.
P1V1=P2V2
In Boyle’s Law, pressure and volume are inversely related.

11. 11
Charles’s Law
Directly relates volume and temperature
V1 = V2
T1 T2

12. 12
Gay-Lussac’s Law
Directly relates pressure and temperature
P1/T1=P2/T2

13. 13
Combined Gas Law
Equation?
P1V1 = P2V2
T1 T2

14. Ideal Gas Law
Allows for us to also solve for moles (n) within a gas
PV = nRT
where R is a constant (0.0821 Lxatm/molxK)

15. Examples
1) A sample of gas at 47°C and 1.03 atm occupies a
volume of 2.20 L. What volume would this gas
occupy at 107°C and 0.789 atm?
Q: Which Gas Law? A:

16. Examples
2) To what temperature must a sample of nitrogen at
27°C and 0.625 atm be taken so that it’s pressure
becomes 1.125 atm at constant volume?
Q: Which Gas Law? A:

17. Examples
3) A meteorological balloon contains 250.0 L He at
22°C and 740.0 mm Hg. What volume will it occupy
at an altitude at which the temperature is -52°C and
the pressure is 0.750 atm?
(hint: notice the differing units of pressure)
Q: Which Gas Law? A:

18. 18
Graham’s Law of Effusion
 Basically states that the
rates of a gases effusion
(?) at the same
temperature and
pressure is inversely
proportional to the square
roots of their molar
masses  EXPLAIN…
 Square root of Molar
Mass A/Square root of
Molar Mass B

19. 19
Avogadro’s Law
States that equal volumes of gases at the same
temperature and pressure contain equal number of
molecules. (and remember that the magic number for
volume of one mole of any gas at STP is… )22.4 L

20. 20
Quiz! 
 Find the mass of each of the following:
 A) 5.60L O2 at 1.75 atm and 250.0K
 B) 3.50 L NH3 at 0.921 atm and 27°C
 C) 125 mL SO2 at 0.822 atm and -5°C