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Properties of Gases

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(torr) after Torricelli, the inventor of the mercury barometer (1643) ... of CO gas has a volume of 25.0 L at a pressure of 789 torr and a temperature of 20oC. ... – PowerPoint PPT presentation

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Title: Properties of Gases


1
Properties of Gases
  • Gases may be compressed.
  • Gases expand to fill their containers uniformly.
  • All gases have low density.
  • Gases may be mixed.
  • A confined gas exerts constant pressure on the
    walls of its container uniformly in all
    directions.

2
Fig. 4-2, p. 97
3
Kinetic Molecular Theory
  • Matter is composed of tiny particles (atoms,
    molecules or ions) with definite and
    characteristic sizes that never change.
  • The particles are in constant random motion, that
    is they possess kinetic energy. Ek 1/2 mv2
  • The particles interact with each other through
    attractive and repulsive forces (electrostatic
    interactions), that is the possess potential
    energy. U mgh
  • The velocity of the particles increases as the
    temperature is increased therefore the average
    kinetic energy of all the particles in a system
    depends on the temperature.
  • The particles in a system transfer energy form
    one to another during collisions yet no net
    energy is lost from the system. The energy of
    the system is conserved but the energy of the
    individual particles is continually changing.

4
Fig. 4-3, p. 98
5
Fig. 4-4, p. 98
6
PRESSURE
  • A physical property of matter that describes the
    force particles have on a surface. Pressure is
    the force per unit area, P F/A
  • Pressure can be measured in
  • atmosphere (atm)
  • millimeters of mercury (mmHg)
  • (torr) after Torricelli, the inventor of the
    mercury barometer (1643)
  • pounds per square inch (psi)
  • 1 atm 760 mmHg 760 torr 14.69 psi

7
Fig. 4-13, p. 109
8
Fig. 4-6, p. 100
9
TEMPERATURE
  • A physical property of matter that determines the
    direction of heat flow.
  • Measured on three scales.
  • Fahrenheit oF Celsius
    oC
  • Kelvin K
  • oF (1.8 oC) 32 oC (oF - 32)/1.8
  • K oC 273.15

10
Fig. 4-1, p. 96
11
  • EMPIRICAL GAS LAWS
  • Boyles Law P1V1 P2V2
  • Charles Law V1 / T1 V2 / T2
  • Combined Gas Law P1V1 / T1 P2 V2 / T2

12
Boyles Law For a fixed quantity of gas at
constant temperature, pressure is inversely
proportional to volume.
Fig. 4-12, p. 108
13
Fig. 4-11a, p. 107
14
Fig. 4-10, p. 106
15
Charless Law The volume of a fixed quantity of
gas at constant pressure is directly proportional
to absolute temperature.
Fig. 4-9, p. 105
16
Empirical Gas Laws
  • 1. At 25oC, a sample of N2 gas under a pressure
    of 689 mmHg occupies 124 mL in a piston-cylinder
    arrangement before compression. If the gas is
    compressed to 75 of its original volume, what
    must be the new pressure (in atm) at 25oC?
  • First make a list of the measurements made
  • P1689 mmHg V1 124 mL
  • P2 ? V2 75 V1
  • From the variables, choose the appropriate
    equation, in this case Boyles Law P1V1P2V2
  • (689 mmHg) (124 mL) P2 (0.75 x 124 mL)
  • Solve for P2
  • P2 (689mmHg) (124 mL) / (93 mL) 919 mmHg
  • Now convert to atm
  • 919 mmHg (1 atm / 760 mmHg) 1.21 atm

17
Empirical Gas Laws
  • 2. The gas in a Helium filled ball at 25oC
    exerts a volume of 4.2 L. If the ball is placed
    in a freezer and the volume decreases to 1/8 of
    its original value, what is the temperature
    inside the ball?
  • First make a list of the measurements made
  • V14.2 atm T1 25 oC 273.15 298.15
  • V2 1/8 P1 T2 ?
  • From the variables, choose the appropriate
    equation, in this case Charles Law V1/T1V2/T2
  • (V1) / (298 K) (1/8 V1) / T2
  • Solve for T2
  • T2 (298 K) (1/8 V1) / (V1) 298 / 8
    37.3 K or -235 oC

18
Empirical Gas Laws
  • A balloon containing 6.50 grams of NH3 has a
    volume of 10.30 L at a temperature of 20.0oC and
    a pressure of 689.2 torr. What would be the
    pressure of NH3 if the volume decreased to 2.50 L
    without a change in temperature?
  • A sample of CO gas has a volume of 25.0 L at a
    pressure of 789 torr and a temperature of 20oC.
    What must the temperature be if the pressure was
    unchanged but the volume needed to be increased
    to 95.0 L?

19
p. 110
20
COMBINED GAS LAW
  • A gas occupies a volume of 720 mL at 37oC and 640
    mmHg pressure. Calculate the volume the gas would
    occupy at 273 K and 1 atm.
  • P1V1 / T1 P2V2 / T2
  • rearranged to solve for V2 is
  • V2 P1 V1 T2 / P2 T1
  • V2 (640 mmHg)(720 mL) (273 K) / (760 mmHg)
    (310 K)
  • V2 534 mL

21
COMBINED GAS LAW
  • What would be the volume at STP of 3.62 liters of
    nitrogen gas, measured at 649 torr and 16 C?
  • P1V1 P2V2 rearranged to solve for V2 is
  • T1 T2
  • V2 P1 V1 T2 V2 (649 torr)(3.62 L)
    (273 K)
  • P2 T1 (760 torr)
    (16 273K)
  • V2 2.92 L

22
COMBINED GAS LAW
  • A gas occupies a volume of 720 mL at 37oC and 640
    mmHg pressure.
  • Calculate the pressure if the temperature is
    increased to 1000oC the volume expands to 900
    mL.
  • Calculate the temperature if the pressure is
    decreased to 10 torr the volume is reduced to
    500 mL.

P2 2.1 x 103 mmHg
T2 3.4 K or -270 oC
23
PRACTICE PROBLEM 20a
1. You prepared carbon dioxide by adding
aqueous HCl to marble chips, calcium carbonate.
According to your calculations, you should obtain
79.4 mL of carbon dioxide at 0 oC and 760 mmHg.
How many milliliters of gas would you obtain at
27oC at the same pressure? 2. Divers working
from a North Sea drilling platform experiences
pressures of 50 atm at a depth of 5.0 x 102 m.
If a balloon is inflated to a volume of 5.0 L
(the volume of a lung) at that depth at a water
temperature of 4.0oC, what would the volume of
the balloon be on the surface (1.0 atm) at a
temperature of 11 oC? 3. What volume would
5.30 L of H2 gas at 0 oC and 760 mmHg occupy if
the temperature was increased to 70oF and the
pressure to 830 torr? 4. The pressure gauge
reads 125 psi on a 0.140-m3 compressed air tank
when the gas is at 33.0 oC. To what volume will
the contents of the tank expand if they are
released to an atmospheric pressure of 751 torr
and a temperature of 13oC? 5. A gas has a
volume of 397.0 mL at 14.70 atm. What will be
its pressure (in torr) if the volume is changed
to 4.100 L?
87.3 mL
256 L
5.23 L
1.126 m3
1082 torr
24
PRACTICE PROBLEM 20a
  • 6. Which of the following statements is false?
  • a) If the Celsius temperature is doubled, the
    pressure of a fixed volume of gas would double.
  • b) All collisions between gas molecules are
    perfectly elastic (no energy is lost) according
    to KMT.
  • c) The volume of gas is inversely proportional
    to the temperature of gas present (P constant)
  • d) Gases are capable of being greatly
    compressed.
  • 7. Which of the following statements are true?
  • a) In a large container of O2 gas the pressure
    exerted by the oxygen will be greater at the
    bottom of the container.
  • b) Of the three states of matter, gases are the
    most compact and the most mobile.
  • c) The formula of ozone is 3 O2.
  • d) Molecules of O2 gas and H2 gas at the same
    temperature will have the same average kinetic
    energies and the same average velocities.

C
D
25
GROUP STUDY PROBLEMS
1. A sample of O2 gas initially at 0oC and 1.0
atm is transferred from a 2-L container to a 1-L
container at constant temperature. a) What
effect does this change have on the average
kinetic energy of the gas molecules? b) What
effect does the total number of collisions of O2
molecules with the container walls in a unit
time? 2. At constant pressure, a student needed
to decrease a volume of 155 mL of Ne gas by
32.0. To what temperature, (in oC), must the
gas be cooled if the initial temperature was
21oC? 3. A sample of CO2 gas has a volume of
125.0 L at a pressure of 789 torr and a
temperature of 30oC. What will be the
temperature if the pressure was increased to 900
torr the volume decreased to 95.0 L? 4. F2 gas,
which is dangerously reactive, is shipped in
steel containers of 30.0 L capacity, at a
pressure of 10.0 atm at 26.0 oC. What should be
the volume of the tank if the pressure is
increased to 820.0 torr the temperature is 43.0
oC?
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