1. Gases

2. Kinetic Molecular Theory
The kinetic molecular theory is used to explain
the behavior of gases.
All matter is made up of particles called atoms.
The atoms are in constant motion.
Collisions between the particles are elastic (no energy is gained or lost due to the collision).

3. Properties used to describe gases.
The following four properties are used to
describe gases:
Temperature (oC or K)-how fast the particles making up the gas are moving.
Volume (L)-the amount of space the gas occupies (usually the size of the container)
Amount of sample (moles)-# of particles in the sample
Pressure (atm, kPa, mm Hg, torrs)

4. Pressure Pressure is the force that is exerted on a surface. P = F/A
Units for pressure are N/m2
One pascal (Pa) = 1 N/m2
Since the pascal is a very small unit, the kPa is more commonly used.
1 kPa = 1000 Pa

5. Practice Problem
A car tire makes contact with the ground on a rectangular area of .12 m x .18 m. If the car’s mass is 9300 N, what pressure does it exert on ground as it rests on all four tires?

6. Gases and Pressure
Gases exert pressure due to the collisions between the molecules and the walls of the container.
The atmosphere exerts a pressure of
14.7 lbs/in2.
Gravity acts as the atmosphere’s container.

7. The atmosphere exerts a pressure that can support a column of mercury 760 mm tall.
1 atm of pressure = 760 mm Hg = 14.7 lbs/in2 = kPa

8. Complete the following conversion problems:
Convert 2.2 atm to kPa.
Convert 750 torrs to atm.
Convert kPa to mmHg.
Convert 10.5 lbs/in2 to atm.

9. Measuring Pressure
The device used to measure pressure is a manometer. A barometer is a specific type of manometer used to measure air pressure.
Open Manometer
Closed Manometer

10. Manometer Problems

11. The Components of the Atmosphere
The atmosphere consists of the following gases:
Nitrogen (N2) = 78%
Oxygen (O2) = 21 %
Argon (Ar) = 0.93%
Carbon Dioxide (CO2) = 0.038%

12. The Structure of the Atmosphere
The atmosphere consists of five principal layers (starting closest to the earth and moving outward):
Troposphere (<20 km): where weather occurs, planes fly, etc.
Stratosphere (20-50 km) : where ozone layer is located, weather balloons fly, etc.
Mesosphere (50-85 km): where most meteors burn up
Thermosphere ( km): International Space Station located here, aurora borealis , etc.
Exosphere (690-10,000 km): mostly consists of hydrogen and helium

13. Layers of the atmosphere

14. Gas Laws

15. Boyle’s Law
At constant temperature, the pressure and volume of a gas are inversely related. (The number of gas particles remains constant).
As pressure increases, volume decreases.
Examples/Applications of Boyle’s Law:
Opening a soft drink bottle
Ears popping when an airplane
takes off
A bicycle pump
Scuba diving

16. Predicting Pressure and Volume Using Boyle’s Law
P1 x V1 = P2 x V2
P1: Original/Starting Pressure
V1: Original/Starting Volume
P2: New/Resulting Pressure
V2: New/Resulting Volume

17. The volume of a gas at 99. 0 kPa is 300. 0 mL
The volume of a gas at 99.0 kPa is mL. If the pressure is increased to 188 kPa, what will be the new volume?
P1 = 99.0 kPa
V1 = mL
P2 = 188 kPa
V2 = ?
P1 x V1 = P2 x V2
(99.0) (300.0) = (188) x
X = 158 mL
(The pressure increased, so the volume decreased).

18. Charles’ Law
At constant pressure, the Kelvin temperature and volume of a gas are directly related. (The number of gas particles remains constant).
As temperature increases, volume increases.
Examples/Applications of Charles’ Law:
Bread rising in the oven
Car tires appearing to be flat in the morning
A balloon pops if left in a hot car

19. Predicting Temperature and Volume Using Charles’ Law
V1 = V2
T T2
V1: Original/Starting Volume
T1: Original/Starting Temperature (Kelvin)
V2: New/Resulting Volume
T2: New/Resulting Temperature (Kelvin)

20. A helium balloon in a closed car occupies a volume of 2. 32 L at 40
A helium balloon in a closed car occupies a volume of 2.32 L at 40.0oC. If the car is parked on a hot day and the temperature inside rises to 75.0oC, what is the new volume of the balloon (assuming the pressure remains constant)?
V1= 2.32 L
T1 = 40.0o = 313 K
T2 = 75.0o = 348 K
V2 = ?
V1 = V2
T T2
2.32 = x
x = L
(The temperature increased, so the volume increased also)

21. Gay-Lussac’s Law
At constant volume, the Kelvin temperature and pressure of a gas are directly related. (The number of gas particles remains constant).
As temperature increases, pressure increases.
Everyday Examples/Applications of Gay-Lussac’s Law:
An aerosol can explodes if left in a fire.
A pressure cooker

22. Predicting Temperature and Pressure Using Gay-Lussac’s Law
P1 = P2
T T2
P1: Original/Starting Pressure
T1: Original /Starting Temperature (in Kelvin)
P2: New/Resulting Pressure
T2: New/Resulting Temperature

23. A cylinder contain a gas which has a pressure of 125kPa at a temperature of 200 K. Find the temperature of the gas which has a pressure of 100 kPa.
P1 = 125 kPa
T1 = 200 K
P2 = 100 kPa
T2 = ?
P1 = P2
T1 T2
125 = 100 x
X =

24. Avogadro’s Principle
Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.
1 mole of any gas at standard temperature (0oC) and pressure (1 atm) occupies 22.4 L of space. (STP)
22. 4 L is known as the molar volume.

25. What is the volume of 2 moles of H2 at STP?

26. Predicting Volume and Moles of Gases Using Avogadro’s Principle.
V1 = V2
n n2
V1 : Original/Starting Volume
n1 : Original/Starting Number of Moles
V2 : New/Resulting Volume
n2: New/Resulting Number of Moles

27. What size container do you need to hold 0.05 moles of N2 gas at STP?
V1 = ?
n1 = 0.05 moles
V2 = 22.4 L
n2 = 1 mole
V1 = V2
n1 n2
x = 22.4
X = 1.12 L

28. Combined Gas Law
The combined gas law states the relationship among pressure, temperature, and volume of a fixed amount of gas.
All three variables have the same relationship to each other as they have in the other gas laws.
This law can be represented by the following equation:
V1P1 = V2P2
T1 T2

29. Practice Problem
A sample of air in a syringe exerts a pressure of 1.02 atm at 22.0oC. The syringe is placed in a boiling water bath at 100.0oC. The pressure is increased to 1.23 atm by pushing the plunger in, which reduces the volume to mL. What was the initial volume?
P1 = 1.02 atm P1V1 = P2V2
T1 = 22.0oC = 295 K T T2
V1=?
P2 = 1.23 atm (1.02)(x) = (1.23)(0.224)
T2 = 100.0oC + 273= K
V2 = mL x = mL

30. Graham’s Law
Diffusion is the term used to describe the movement of one material through another.
Effusion is a term used to describe the escape of a gas through an opening.
Example: Helium will effuse through a hole in a balloon.
Graham’s law states that the rate of effusion for a gas is inversely proportional to the square root of its molar mass.
In other words; the heavier the gas, the slower it’s rate of effusion.

31. Predicting Rates of Effusion Using Graham’s Law
Rate of gas A =
Rate of gas B
Molar Mass of B
Molar Mass of A

32. Which will deflate faster; a balloon filled with carbon dioxide or a balloon filled with helium?
Rate of gas A =
Rate of gas B
Gas A is Helium (He)
Gas B is Carbon Dioxide (CO2)
Molar mass of CO2 = 44 g
Molar mass of He = 4 g
44/4
Helium diffuses 3.31 times faster
Molar Mass of B
Molar Mass of A

33. Dalton’s Law of Partial Pressures
The total pressure of a mixture of gases is equal to the sum of the pressures of all of the gases in the mixture.
Ptotal = P1 + P P3 + …
A mixture of oxygen, nitrogen and hydrogen gases have a total pressure of 0.97 atm. What is the partial pressure of oxygen if the partial pressure of nitrogen is 0.70 atm and the partial pressure of hydrogen is 0.12 atm?
0.97 = x
0.15 atm

34. Ideal Gas Law
The ideal gas law is a mathematical equation that describes the relationship among all 4 properties.
The formula works best when gases obey the assumptions of the kinetic molecular theory.
PV = nRT
P is pressure; V is volume in liters; T is temperature in Kelvin; n is the number of moles; and R is the gas constant
R = if pressure is in kPA; R= if pressure is in atm; R= 62.4 if pressure is in mm Hg or torrs.

35. Calculate the number of moles of ammonia gas contained in a 3
Calculate the number of moles of ammonia gas contained in a 3.0 L container at 300. K with a pressure of 1.50 atm.
V = 3.0 L
P = 1.50 atm
T = 300. K
R =
n = ?
PV = nRT
(1.50)(3.0) = x (0.0821)(300)
X = 0.18 mol