The Nature of Gases by KeWjCeJx

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									    Chapter 12
      Gases

Properties of Gases
   Gas Pressure




     LecturePLUS Timberlake   1
                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




              LecturePLUS Timberlake              3
      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
                   LecturePLUS Timberlake              4
      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
              LecturePLUS Timberlake       5
          Nature of Gases

 Gases fill a container completely and
  uniformly

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




               LecturePLUS Timberlake     6
         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

                    LecturePLUS Timberlake        7
           Barometers

                                     760 mmHg



atm
pressure




            LecturePLUS Timberlake          8
          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

                 LecturePLUS Timberlake   9
               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

                 LecturePLUS Timberlake            10
           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

                 LecturePLUS Timberlake   11
         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)

                LecturePLUS Timberlake    12
                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
                  LecturePLUS Timberlake     13
  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

                  LecturePLUS Timberlake            14
            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

                   LecturePLUS Timberlake      15
                 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)

                  LecturePLUS Timberlake     16
     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


              LecturePLUS Timberlake     17

								
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