Gases

1
Chapter 11

• Gases

We live immersed at the bottom of a sea of
elemental air. Evangelista Torricelli
2
(No Transcript)
3
(No Transcript)
4
(No Transcript)
5
Properties of Gases

• Gases form homogeneous mixtures
• Gases are compressible
• All gases have low densities
• air 0.0013 g/mL
• water 1.00 g/mL
• iron 7.9 g/mL
• Gases expand to fill their containers uniformly
• A gas exerts a pressure

6
(No Transcript)
7
(No Transcript)
8
(No Transcript)
9
(No Transcript)
10
Pressure

• Defined as force per unit area

11
(No Transcript)
12
Pressure Units

• 101.325 kPa
• 760 mmHg
• 760 torr
• 1 atm
• 30 in Hg
• 14.7 psi

13
(No Transcript)
14
Measurement of Pressure
15

• The atmospheric pressure at the summit of Mt.
  McKinley (Denali) is 606 mm Hg on a certain day.
  What is the pressure in atmospheres?

16
The Gas Laws
Jacques-Alexandre-César Charles(1746-1823)
Amadeo Avogadro (1776-1856)
Robert Boyle (1627-1691)
17
Boyles Law

• The volume of a gas and its pressure are
  inversely proportional.

18
P1V1 P2V2

• An inflated balloon has a volume of 0.55 L at sea
  level (1.0 atm) and is allowed to rise to a
  height of 6.4 km, where the pressure is about
  0.40 atm. Assuming that the temperature remains
  constant, what is the final volume of the
  balloon?

19
P1V1 P2V2

• A 1.04 L sample of gas at 759 mm Hg pressure is
  expanded until its volume is 2.24 L. What will
  be the pressure in the expanded gas sample if the
  temperature remains constant?

20
Charles Law

• The volume (V) of a gas and its temperature (T)
  expressed in kelvin are directly proportional.

21
V1/T1V2/T2

• A container of 452 mL of argon is heated from
  22oC to 187oC at constant pressure. What is its
  final volume?

22
V1/T1V2/T2

• Gas volume is sometimes used as a way to measure
  temperature. Suppose a sample of a gas in a
  thermometer has a volume of 135 mL at 11oC. What
  temperature would correspond to a volume of 113
  mL?

23
Avogadros Law

• The volume of a gas and the amount of the gas in
  moles(n) are directly proportional.

24
V1/n1V2/n2

• If 3.25 mol of argon gas occupies a volume of
  100.0 L at a particular temperature and pressure,
  what volume does 14.15 mol of argon occupy under
  the same conditions?

25
From V? T Charles Law V ? n Avogadro Law V ?
1/P Boyles Law Get
26
Ideal Gas Law

• PV nRT
• P pressure (typical units are atm or torr or mm
  Hg)
• V volume (typical units are L)
• n number of moles
• T temperature (must be in K)
• R gas constant 0.0821 L atm/mol K
• 62.4 L torr/mol K

27

• A sample of nitrogen gas kept at 32oC in a 2.3 L
  container exerts a pressure of 4.7 atm.
  Calculate the number of moles of gas present.

28

• Calculate the volume in liters occupied by 7.40 g
  of CO2 at 735 torr and 25oC.

29

• A bicycle tire has a pressure of 2000 torr in
  Death Valley when the temperature is 38oC. What
  would the pressure be if you took the bike to
  Lake Tahoe where the temperature was 0oC?

30

• What will be the new volume if 125 mL of He gas
  at 100oC and 0.981 atm is cooled to 25oC and the
  pressure is increased to 1.15 atm?

31

• Find the molar mass of an unknown gas that has a
  density of 1.45 g/L at 44oC and 0.331 atm.

32
Standard Temperature and Pressure (STP)

• T 0oC 273K
• P 1 atm 760 torr

33

• Calculate the volume of 1.0 mole of a gas at STP.
• What volume will 3.21 moles of Ne occupy at STP?

34

• Calculate the density of Argon at STP.

35
Daltons Law of Partial Pressures

• Ptotal P1 P2 P3 ......
• The total pressure of a gas mixture is equal to
  the sum of the pressures of the individual gases.

36

• The atmosphere of Venus contains the following
  gases.
• CO2 392 torr,
• N2 834 torr
• Ar 302 torr
•  
• What is the atmospheric pressure on Venus?

37

• In 1774, Joseph Priestly heated mercury(II) oxide
  by using a lens to focus the rays of the sun on a
  sample of the red powder. It decomposed into its
  elements, and thus oxygen was discovered
•  
• 2 HgO(s) ? 2 Hg(l) O2(g)
•  
• Calculate the volume of oxygen, adjusted to STP,
  that is produced by decomposing 71.8 g HgO.

38

• Dolomite, the white rock used in gardens, is a
  one to one combination of calcium and magnesium
  carbonate. Another use is the manufacture of
  refractory brick for lining very-high-temperature
  furnaces. It is processed through a rotary kiln
  in which carbon dioxide is driven off
• CaCO3?MgCO3(s) ? CaO(s) MgO(s) 2 CO2(g)
• For each kilogram of dolomite processed, how many
  liters of carbon dioxide escape to the atmosphere
  at 264oC and 1.09 atm?

39

• Sulfur burns to SO2 with a beautiful deep
  purple-blue flame, but with a foul, suffocating
  odor
•   2 S(s) O2(g) ? 2 SO2(g)
•  How many liters of O2 are needed to form 35.2 L
  SO2, both gases being measured at 741 torr and
  26oC?

40

• A 3/4 full propane tank has a pressure of 3.2 atm
  at a temperature of 25oC. If you put the tank in
  the back of your car for a barbecue at the beach
  and the temperature reaches 103oC, what is the
  new pressure of the propane in the tank?

41

• What volume will 4.83 moles of a gas occupy at
  35oC and 1.15 atm pressure?

42

• The nitrogen gas in an air bag with a volume of
  35 L, exerts a pressure of 850 mm Hg at 25oC.
  How many moles of N2 are in the bag?

43

• Sulfur hexafluoride (SF6) is a colorless,
  odorless, very unreactive gas. Calculate the
  pressure (in atm) exerted by 1.82 moles of the
  gas in a steel vessel of volume 5.43 l at 69.5oC.