Unit 4 – Gases
Section 1 – Kinetic Molecular Theory
Characteristics of Gases
1. Why do all gases have very similar physical properties but very different chemical properties?
Gases have similar physical properties because they are all in the same phase and very spread out. They have different chemical properties
because they have different electron arrangements.
2. What is the approximate pressure (in atmospheres) at sea level? 1.0 atm
3. What is standard pressure (in atmospheres)? 1.0 atm
4. What are the equivalent pressures in the other main units of pressure?
1.0 atm = 760 torr = 101,325 Pascal = 101.35 kPa = 1.01325 bar = 760 mmHg = 14.7 psi
5. Draw a picture of a barometer and label its parts.
See picture.
Partial Pressures
6. A gaseous mixture of 6.00 g of oxygen and 9.00 grams of methane are in a container with a total pressure of 1.12
atm.
a. What is the partial pressure of each gas in atm?
6.00 g O 2 1 mol
9.00 g CH 4 1 mol

 0.1875 mol

 0.5625 mol
1
32.00 g
1
16.00 g
25% oxygen 75% methane
0.28 atm of oxygen and 0.84 atm of methane
b. What is the mole fraction of each gas?
0.25 oxygen and 0.75 methane
7. A flask contains Ne at 542 mmHg together with Ar at 234 mmHg.
a. What will the total pressure be? 776 mmHg
b. What is the mole fraction of each gas? 0.698 Ne and 0.301 Ar
c.
If there are 10 grams of gas in the container, how many grams of each gas are present?
2.3189 x(20.180)  x(39.948)  10  x  0.11528
0.2673 mol Ne = 5.39 g Ne
and
0.11528 mol Ar = 4.51 g Ar
Kinetic Molecular Theory
8. In the Kinetic Molecular Theory reading, there is a list of 5 different aspects of kinetic
molecular theory of gases. Draw a picture (or pictures) that represents all 5 of the statements.
9. If you have a container of CO2, N2, and O2, all at the same temperature, list them in order of increasing average
kinetic energy. They all have the same average kinetic energy.
10. If you have a container of CO2, N2, and O2, all at the same temperature, list them in order of increasing average
speed. The lighter gases are going to have faster speeds: N2 < O2 < CO2
Graham’s Law of Effusion
11. Compare and contrast diffusion and effusion. They both deal with gases moving, effusion is moving through a small hole,
diffusion is moving from high to low density.
12. A pure sample of methane is found to effuse e through a porous barrier in 1.50 minutes. Under the same
conditions, an equal number of molecules of an unknown gas effuses through the barrier in 4.73 minutes. What
is the molar mass of the unknown gas?
4.73
x
x
x

 3.153 2 
 9.9435 
 x  159 g/mol
1.50
16
16
16