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									Chapter 11

GASES
If force is held constant as surface area decreases,
  pressure
a.remains constant.
b.decreases.
c.increases.
d.increases or decreases, depending on the volume
  change.
Why does a can collapse when a vacuum pump
  removes air from the can?
a.The inside and outside forces balance out and crush
  the can.
b.The unbalanced outside force from atmospheric
  pressure crushes the can.
c.The atmosphere exerts pressure on the inside of the
  can and crushes it.
d.The vacuum pump creates a force that crushes the
  can.
If the height of mercury in a barometer at 0ºC is less
  than 760 mm Hg, then
a.the atmospheric pressure is less than standard
  atmospheric pressure.
b.the atmospheric pressure is greater than standard
  atmospheric pressure.
c.the atmospheric pressure is equal to standard
  atmospheric pressure.
d.the atmospheric pressure cannot be determined.
Convert the pressure 0.840 atm to mm Hg.
a.365 mm Hg
b.437 mm Hg
c.638 mm Hg
d.780 mm Hg
Convert the pressure 1.30 atm to kPa.
a.2 kPa
b.115 kPa
c.132 kPa
d.245 kPa
Standard temperature is exactly
a.100ºC.
b.273ºC.
c.0ºC.
d.0 K.
To correct for the partial pressure of water vapor in a
  gas collection bottle, the vapor pressure of H2O at
  the collecting temperature is generally
a.subtracted from the partial pressure of the collected
  gas.
b.added to the pressure of the collected gas.
c.subtracted from the atmospheric pressure.
d.added to the atmospheric pressure.
Three samples of gas each exert 740. mm Hg in
  separate 2 L containers. What pressure do they exert
  if they are all placed in a single 2 L container?
a.247 mm Hg
b.740 mm Hg
c.1.48 x 103 mm Hg
d.2.22 x 103 mm Hg
The volume of a gas is 400.0 mL when the pressure is
  1.00 atm. At the same temperature, what is the
  pressure at which the volume of the gas is 2.0 L?
a.0.5 atm
b.5.0 atm
c.0.20 atm
d.800 atm
If the temperature of a fixed quantity of gas decreases
  and the pressure remains unchanged,
a.its volume increases.
b.its volume is unchanged.
c.its volume decreases.
d.its density decreases.
The volume of a gas is 5.0 L when the temperature is
  5.0ºC. If the temperature is increased to 10.0ºC
  without changing the pressure, what is the new
  volume?
a.2.5 L
b.4.8 L
c.5.1 L
d.10.0 L
Why could the pressure of a sample of gas at a
  constant volume fall 75 mm Hg?
a.The container exploded.
b.The temperature increased.
c.The temperature decreased.
d.The volume increased.
Why does the air pressure inside the tires of a car
  increase when the car is driven?
a.Some of the air has leaked out.
b.The air particles collide with the tire after the car is
  in motion.
c.The air particles inside the tire increase their speed
  because their temperature rises.
d.The atmosphere compresses the tire.
On a cold winter morning when the temperature is –
  13ºC, the air pressure in an automobile tire is 1.5
  atm. If the volume does not change, what is the
  pressure after the tire has warmed to 15ºC?
a.–1.5 atm
b.1.7 atm
c.3.0 atm
d.19.5 atm
The volume of a gas collected when the temperature is
  11.0ºC and the pressure is 710 mm Hg measures 14.8
  mL. What is the calculated volume of the gas at
  20.0ºC and 740 mm Hg?
a.7.8 mL
b.13.7 mL
c.14.6 mL
d.15 mL
                       Gas Volumes

 Gay-Lussac’s Law of Combining Volumes of Gases
   At constant temperature and pressure, the volumes of gaseous
    reactants and products can be expresses as ratios of small
    whole numbers

    hydrogen gas + oxygen gas  water vapor
      2 L (2 volumes) 1 L (1 volume) 2 L (2 volumes)
                    Avogadro’s Law

 Equal volumes of gases at the same temperature
 and pressure contain equal numbers of molecules
    The equation for this relationship is shown below, where
     V is the volume, k is a constant, and n is the amount of
     moles of the gas.


                           V = kn
                  Avogadro’s Law

 Dalton had guessed that the formula for water
 was HO, but Avogadro’s reasoning established that
 water must contain twice as many H atoms as O
 atoms because of the volume ratios in which the
 gases combine:

 hydrogen gas + oxygen gas  water vapor
 2 L (2 volumes) 1 L (1 volume)   2 L (2 volumes)
Gay-Lussac recognized that at constant temperature
  and pressure, the volumes of gaseous reactants and
  products
a.always equal 1 L.
b.add up to 22.4 L.
c.equal R.
d.can be expressed as ratios of small whole numbers.
The law of combining volumes applies only to gas
  volumes
a.measured at constant temperature and pressure.
b.that equal 1 L.
c.that equal 22.4 L.
d.measured at STP.
If 0.5 L of O2(g) reacts with H2 to produce 1 L of
  H2O(g), what is the volume of H2O(g) obtained from
  1 L of O2(g)?
a.0.5 L
b.1.5 L
c.2 L
d.2.5 L
             Molar Volume of a Gas

 Recall that one mole of a substance contains a
 number of particles equal to Avogadro’s constant
 (6.022  1023).

 According to Avogadro’s law, one mole of any gas
 will occupy the same volume as one mole of any
 other gas at the same conditions, despite mass
 differences.
         Molar Volume of a Gas

 The volume occupied by one mole of
 gas at STP is known as the

   standard molar volume of a gas


          which is 22.414 10 L
            (rounded to 22.4 L).
                   Gas Stoichiometry

 The coefficients in chemical equations of gas
 reactions reflect not only molar ratios, but also
 volume ratios (assuming conditions remain the
 same).
 Example-reaction of carbon dioxide formation:
      2CO(g)   +   O2(g)      2CO2(g)
In the reaction represented by the equation N2(g) +
  2O2(g) -> 2NO2(g), what is the volume ratio of N2 to
  NO2?
a.1:1
b.1:2
c.2:1
d.2:5
The equation for the production of methane is C +
  2H2(g) -> CH4(g). How many liters of hydrogen are
  needed to produce 20. L of methane?
a.2.0 L
b.20. L
c.22.4 L
d.40. L
What is the number of moles of H2 produced when 23
  g of sodium react with water according to the
  equation 2Na(s) + 2H2O(l) -> 2NaOH(aq) + H2(g)?
a.0.50 mol
b.1.0 mol
c.2.0 mol
d.4.0 mol
If the temperature of a container of gas remains
  constant, how could the pressure of the gas increase?
a.The mass of the gas molecules increase.
b.The diffusion of the gas molecules increases.
c.The size of the container increases.
d.The number of gas molecules in the container
  increases.
If gas A has a molar mass greater than that of gas B
  and samples of each gas at identical temperatures
  and pressures contain equal numbers of molecules,
  then
a.the volumes of gas A and gas B are equal.
b.the volume of gas A is greater than that of gas B.
c.the volume of gas B is greater than that of gas A.
d.their volumes are proportional to their molar
  masses.
At STP, the standard molar volume of a gas of known
  volume can be used to calculate the
a.number of moles of gas.
b.rate of diffusion.
c.gram-molecular weight.
d.gram-molecular volume.
                      Ideal Gas Law

 It is stated as shown below, where R is a constant:
           PV = nRT
 In the equation representing the ideal gas law, the
  constant R is known as the ideal gas constant.

    Its value depends on the units chosen for pressure,
     volume, and temperature in the rest of the equation.
Ideal Gas Constants
           Sample Problem I



 What is the pressure in atmospheres
 exerted by a 0.500 mol sample of
 nitrogen gas in a 10.0 L container at
 298 K?
Sample Problem I
The ideal gas law is equivalent to Boyle's law when
a.the number of moles and the pressure are constant.
b.R equals zero.
c.the pressure is 1 atm.
d.the number of moles and the temperature are
  constant.
A 1.00 L sample of a gas has a mass of 1.92 g at STP.
  What is the molar mass of the gas?
a.1.92 g/mol
b.19.2 g/mol
c.22.4 g/mol
d.43.0 g/mol
Iron(IV) oxide, FeO2, is produced by the reaction Fe +
  O2 ® FeO2 (87.8 g/mol). How many grams of FeO2
  can be produced from 50.0 L of O2 at STP?
a.19.5 g
b.37.8 g
c.50 g
d.196. g
Calculate the approximate volume of a 0.600 mol
  sample of gas at 15.0°C and a pressure of 1.10 atm.
a.12.9 L
b.22.4 L
c.24.6 L
d.139 L
What is the pressure exerted by 1.2 mol of a gas with a
  temperature of 20.ºC and a volume of 9.5 L?
a.0.030 atm
b.1.0 atm
c.3.0 atm
d.30. atm
      Diffusion and Effusion
 The gradual mixing of two or more gases due to their
 spontaneous, random motion is known as diffusion.

 Effusion is the process whereby the molecules of a
 gas confined in a container randomly pass through a
 tiny opening in the container.
           Graham’s Law of Effusion

 Rates of effusion and diffusion depend on the
 relative velocities of gas molecules. The velocity of a
 gas varies inversely with the square root of its molar
 mass.

    Recall that the average kinetic energy of the molecules in any
     gas depends only the temperature and equals
Graham’s Law of Effusion
Graham’s Law
             Sample Problem

 Compare the rates of effusion of
 hydrogen and oxygen at the same
 temperature and pressure.
            Sample Problem




Hydrogen effuses 3.98 times faster than oxygen.
If a gas with an odor is released in a room, it can
  quickly be detected across the room because it
a.diffuses.
b.is dense.
c.is compressed.
d.condenses.
What is the process by which molecules of a gas
  randomly encounter and pass through a small
  opening in a container?
a.diffusion
b.vaporization
c.distillation
d.effusion
According to Graham's law, two gases at the same
  temperature and pressure will have different rates of
  effusion because they have different
a.volumes.
b.molar masses.
c.kinetic energies.
d.condensation points.
How many times greater is the rate of effusion of
  molecular fluorine than that of molecular bromine at
  the same temperature and pressure?
a.2.051
b.3.062
c.4.450
d.7.280
A sample of hydrogen gas diffuses 3.8 times faster
  than an unknown gas diffuses. What is the molar
  mass of the unknown gas?
a.4.0 g/mol
b.7.6 g/mol
c.22 g/mol
d.29 g/mol

								
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