The Nature of Gases

							    Chapter 12
      Gases

Properties of Gases
   Gas Pressure




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                Gases

What gases are important for each of the
following: O2, CO2 and/or He?

 A.           B.                       C.   D.




              LecturePLUS Timberlake             2
                Gases

What gases are important for each of the
following: O2, CO2 and/or He?

 A. CO2      B. O2/CO2                 C. O2   D. He




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      Some Gases in Our Lives
                           Air:
oxygen O2        nitrogen N2                ozone O3
argon Ar      carbon dioxide CO2   water H2O
                   Noble gases:
helium He     neon Ne krypton Kr    xenon Xe
                   Other gases:
fluorine F2      chlorine Cl2   ammonia NH3
methane CH4      carbon monoxide CO
nitrogen dioxide NO2              sulfur dioxide SO2
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      The Nature of Gases

 Gases are compressible
 Why can you put more air in a tire, but
 can’t add more water to a glass full of
 water?
 Gases have low densities
    Density of solid or liquid = 2 g/mL
    Density of gas 2 g/L
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          Nature of Gases

 Gases fill a container completely and
  uniformly

 Gases exert a uniform pressure on all
  inner surfaces of their containers




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         Kinetic Theory of Gases
The particles in gases

•   Are very far apart

•   Move very fast in straight lines until they
    collide

•   Have no attraction (or repulsion)

•   Move faster at higher temperatures

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           Barometers

                                     760 mmHg



atm
pressure




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          Learning Check G1

1. The downward pressure of the Hg in a
  barometer is _____ than (as) the weight of
  the atmosphere.
     A) greater    B) less       C) the same




            ANSWER: C) the same

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               Solution G1

2. A water barometer has to be 13.6 times
  taller than Hg barometer (DHg = 13.6 g/mL)
 because
 A) H2O is less dense           B) Hg is heavier
 C) air is more dense than H2O


         Answer: A) H2O is less dense

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           Unit of Pressure

 One atmosphere (1 atm)
Is the average pressure of the atmosphere
 at sea level
Is the standard of pressure
 P = Force = N
          Area       m2

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         Learning Check G2
When you drink through a straw you reduce
the pressure in the straw. Why does the liquid
go up the straw?
 A) the weight of the atmosphere pushes it
 B) the liquid is at a lower level
 C) there is empty space in the straw

            Answer: A) and C)

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                Solution G2
  Could you drink a soda this way in outer
space?
A) yes
B) no
C) maybe, but it would be more difficult
Why or why not?

Answer: B) NO, because there is no air pressure to
            push down on the liquid
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  Units of Pressure that = 1 atm
    unit                          Used in
760 mm Hg or 760 torr             Chemistry
101.3 kPa (kilopascals)           metric unit
14.7 lb/in.2                      U.S. pressure gauges
29.9 in. Hg                       U.S. weather reports
1.013 bars                        Physics and
                                  astronomy

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            Converting units

A. What is 475 mm Hg expressed in atm?
  1) 475 atm    2) 0.625 atm 3) 1.60 atm
B. The pressure of a tire is measured as 29.4 psi.
   What is this pressure in mm Hg?
  1) 0.569 mm Hg
  2) 1520 mm Hg
  3) 32,800 mm Hg

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                 Solution G3
A. What is 475 mm Hg expressed in atm?
475 mm Hg    x    1 atm   = 0.625 atm (B)
                  760 mm Hg

B. The pressure of a tire is measured as 29.4 psi.
   What is this pressure in mm Hg?
29.4 psi x 1.00 atm x 760 mmHg = 1.52 x 103 mmHg
           14.7 psi 1.00 atm              (B)

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     Kelvin Temperature
• When using the gas laws, we must use
  the Kelvin scale !!!!!

• 0°C = 273 K (no degree symbol)
• To convert °C to K, add 273
• Ex: Convert 72 °C to Kelvin


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