Chapter 5: Gases

1
Chapter 5 Gases

• Pressure
• The Empirical Gas Laws
• The Ideal Gas Law Its Applications
• Mixtures of Gases
• The Kinetic Molecular Theory of Gases
• Effusion Diffusion
• Real Gases

2
Example 1

• Find the volume of a gas at a pressure of
• 1.5 x 103 mmHg if it has a volume of
• 1.0 L at 1.0 atm.  Assume the
• temperature is unchanged.  
• Answer 0.51 L

3
Example 2

• A sample of CO2 has a volume of 533 mL
• at 23.2ºC and 749 mmHg.  How many
• moles of CO2 are in this sample?
• Answer .0216 moles CO2

4
Example 3

• An experiment calls for 4.00 moles of CO
• gas at STP.  What volume of gas is this?
• Answer 89.7 L

5
Example 4

• For a gas at 25ºC the volume  is 2.0
• L.  Find its volume at 100.ºC if its
• pressure remains constant.
• Answer 2.5 L

6
Example 5

• What is the volume of a sample of
• O2 at 25 ºC and 1.00 atm if it has
• a mass of 1.50 g?
• Answer 1.15 L

7
Example 6

• LiOH is used in spacecraft to absorb the CO2
• exhaled by the astronauts
•    2 LiOH (s)    CO2 (g)  ?  Li2CO3 (s)    H2O
  (l)
• What volume of CO2 can be absorbed by 1.00
• g of LiOH at 25.0C and 1.00 atm?
• Answer 0.511 L

8
Example 7

• What is the density of neon gas in g/L at
• 27ºC and 748 mmHg?
• Answer 0.806 g/L

9
Example 8

• An unknown gas has a density of
• 0.164 g/L at 21ºC and 752 mmHg.
• Find the molecular weight of this
• gas.
• Answer 4.00 g/mole (helium)

10
Example 9

• An experimental undersea habitat had an
• atmosphere consisting of the following mole
• percents
• 79.0 He17.0 N24.0 O2
• What are the partial pressures of each gas at
  58.8 m
• below sea level where the pressure is 6.91 atm?
• Answer 5.46 atm He, 1.17 atm N2, 0.28 atm O2

11
Example 10

• The reaction between zinc metal and
• acid produces hydrogen gas.  Assume
• the hydrogen produced by this reaction
• was collected over water at 753 mmHg
• and at 23ºC.  If 215 mL of hydrogen
• were collected, what mass of hydrogen
• was produced?
• Answer 1.72 x 10-2 g H2

12
Example 11

• Calculate the average kinetic energy for
• 1.00 mole of oxygen gas at 21C.
• Answer 3.67 x 103 J

13
Example 12

• Calculate the average velocity of
• oxygen molecules at 21C.
• Answer 479 m/s

14
Example 13

• It takes 5.28 seconds for 15.0 mL of
• He gas to effuse through a pinhole in a
• container.  It takes 14.9 seconds for
• the same volume of an unknown gas to
• effuse through the same hole under the
• same conditions.  What is the molecular
• weight of the unknown gas?
• Answer 31.9 g/mole (oxygen?)

15
Example 14

• Find the pressure of ethanol vapor at 82ºC if
• 1.00 mole occupies a volume of 35.00 L.  Use
• both the Ideal Gas Law and Van der Waals
• equation and compare your answers.
• a 12.02 L2atm/mole2
• b .08407 L/mole
• Answer 0.832 atm (IGL) 0.825 atm (VDW)

16
Example 15

• Use the Van der Waals equation to find the
• volume of 1.00 g of CO2 at 0ºC and 10.0 atm. 
• a 3.59 L2atm/mole2
• b .0427 L/mole
• (Hint  because this problem results in a cubic
• equation, simplify by using the Ideal gas law to
• estimate V and use this estimate in the
• correction factor to P.  You will be making a
• small error in a small correction term so the
• final result will be very close to the exact
• solution.) Answer 48.5 mL