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CHAPTER 12: GASES AND THEIR PROPERTIES

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Title: CHAPTER 12: GASES AND THEIR PROPERTIES


1
CHAPTER 12 GASES AND THEIR PROPERTIES
  • That this was not the case, I attributed to the
    force of prejudice, which, unknown to ourselves,
    biases not only our judgments, properly so
    called, but even the perceptions of our senses
    for we may take a maxim so strongly for granted,
    that the plainest evidence of sense will not
    entirely change, and often hardly modify, our
    persuasions, and the more ingenious a man is the
    more effectually he is entangled in his errors
    his ingenuity only helping him to deceive
    himself, by evading the force of truth.
  • -Joseph Priestley (1790) recounting the
    discovery of oxygen/gases

2
12.0 OBJECTIVES
  • Describe the properties of gases (volume, amount,
    pressure, temperature), units of measurement, and
    instruments used to measure these quantities.
  • Understand and use the ideal gas law to solve a
    variety of problems.
  • Apply gas laws equations to stoichiometry
    problems.
  • Understand the uses of Daltons Law and Grahams
    Law equations.
  • Use the kinetic molecular theory to describe the
    behavior of gases at the molecular level.
  • Compare the behavior of real gases to ideal gases.

3
HOMEWORK
  • HW1 11, 15, 17, 19, 21, 25, 65
  • Conversions, Boyles, Charles, Combined
  • HW2 27, 29, 31, 33, 37, 63, 75, 99
  • Ideal Gas Law, Gas Density
  • HW3 41, 45, 71, 85, 105
  • Gas Stoichiometry
  • HW4 47, 49, 97, 103
  • Partial Pressures
  • HW5 51, 55, 59, 61
  • Kinetic-Molecular, Diffusion, Nonideal Gases

4
12.1 PROPERTIES OF GASES
  • 1. Study of gases as a separate unit in
    chemistry
  • In the gas phase, all substances are remarkably
    similar and easily described by the kinetic
    molecular theory.
  • Factors that affect gases are easy to describe
    and measure.
  • Universal simple mathematical relationships apply
    to all gases.

5
12.1 PROPERTIES OF GASES
  • 2. Four inter-related variables associated with
    gases
  • a. Volume V
  • Gases take up a large volume
  • Usually measured in L
  • 1 mol 22.4 L _at_ STP
  • b. Amount of gasn
  • Measured in moles

6
12.1 PROPERTIES OF GASES
  • c. TemperatureT
  • ENERGY! (avg. kinetic energy of particles)
  • Impacts properties of gas
  • Measured in K (Kelvin) KC273.15

7
12.1 PROPERTIES OF GASES
  • d. PressureP
  • 1. Cause of pressure
  • Atmosphere composed of gas molecules
  • Mass of all of these cause pressure (Force/area)

8
12.1 PROPERTIES OF GASES
  • 2. Units of pressure
  • Torr (mmHg), Atmosphere (atm), Pascal (Pa)
    N/m2, Bar, inHg
  • 1 atm 760 torr 101.3 kPa 1.013 bar 29.92
    inHg
  • STP
  • Standard Temperature and Pressure
  • 1 atm (760 torr) 273 K (0oC)

9
12.1 PROPERTIES OF GASES
  • 3. Measuring Pressure
  • a. Manometer and Barometer
  • Device used to measure pressure

10
12.1 PROPERTIES OF GASES
11
12.1 PROPERTIES OF GASES
  • Manometer Problems
  • Just follow along ?

12
12.1 PROPERTIES OF GASES
13
12.1 PROPERTIES OF GASES
14
12.1 PROPERTIES OF GASES
15
12.1 PROPERTIES OF GASES
  • b. Altitude and barometric pressure
  • What do YOU think the trend is?

16
12.1 PROPERTIES OF GASES
  • 4. Ex12.1 Express 753 mmHg in atm, kPa, and
    bars.

17
12.2 GAS LAWS EXPERIMENTAL BASIS
  • 1. Proportions
  • a. Direct
  • As one term increases, so does the other
  • X 1
  • Y
  • b. Inverse
  • As one term increases, the other decreases
  • XY 1

18
12.2 GAS LAWS EXPERIMENTAL BASIS
  • 2. Volume and Pressure, T and n constant -
    Boyle's Law
  • For a given amount of gas at constant
    temperature, the volume is inversely proportional
    to the Pressure
  • P1V1 P2V2

19
12.2 GAS LAWS EXPERIMENTAL BASIS
  • Ex12.2 When an auto airbag inflates as a result
    of an accident, the gases inside are at a final
    volume of 25.0L and pressure of just over
    atmospheric pressure, 780mmHg. What is the
    pressure in the uninflated bag with a volume of
    1.00L?

20
12.2 GAS LAWS EXPERIMENTAL BASIS
  • Volume and Temperature, n and P constant -
    Charles Law
  • The volume of a gas is directly proportional to
    the temperature (in Kelvin) at constant pressure
    and amount of gas
  • V1 V2
  • T1 T2

21
12.2 GAS LAWS EXPERIMENTAL BASIS
  • Volume and moles, T and P constant Gay-Lussacs
    Law
  • Volume is directly proportional to of moles
  • of molecules ? ? Volume ?
  • So, coefficients in a balanced equation involving
    gases are also the volume ratio

22
12.2 GAS LAWS EXPERIMENTAL BASIS
  • 6. Temperature and Pressure, n and V constant
    Amontons Law
  • The temperature is directly proportional to the
    pressure
  • P1 P2
  • T1 T2

23
12.2 GAS LAWS EXPERIMENTAL BASIS
  • 7. Combined Gas Law
  • _P1V1_ _P2V2_
  • n1T1 n2T2

24
12.2 GAS LAWS EXPERIMENTAL BASIS
  • Ex12.3 A gas occupies a volume of 7.50L at
    300.mmHg and 200.0oC. What is its volume if the
    same sample of gas is at a pressure of 1.50atm
    and at a temperature of 22.0oC?

25
12.2 GAS LAWS EXPERIMENTAL BASIS
  • 9. Avogadro's Hypothesis
  • Equal volumes of gases at the same Temp. and
    Pressure have the same number of molecules

26
12.2 GAS LAWS EXPERIMENTAL BASIS
  • 10. Derivation of Volume-moles relationship
  • Compared masses of equal volumes of different
    gases and determined weight ratios? atomic
    weights.
  • Avogadro molded together Daltons atomic theory
    with Gay-Lussacs law of combining volumes
  • Avogadro threatened Daltons ideas about
    atom/molar masses? work was ignored for 50 years!

27
12.2 GAS LAWS EXPERIMENTAL BASIS
  • Ex12.4 Given the Haber reaction below a. What
    volume of hydrogen is required to form 12.0L of
    ammonia? b. What volume of nitrogen gas is
    necessary to react completely with 1.41 Liters of
    hydrogen gas? Assume constant T and P.
  • 3H2(g) N2(g) ? 2NH3(g)

28
12.3 IDEAL GAS LAW
  • 1. Derivation of Ideal Gas Law
  • Combination of Boyles, Charles, and Avogadros
    Laws
  • PV nRT

29
12.3 IDEAL GAS LAW
  • 2. Value of the gas law constant, R
  • R .0821 Latm R 8.314 J
  • molK molK

30
12.3 IDEAL GAS LAW
  • 3. Ex12.5 Will it be safe to store 2500g of
    oxygen gas in a 10.0L container at 20.0oC if the
    container is built to a tolerance of 200atm?

31
12.3 IDEAL GAS LAW
  • 4. Ex12.6 Calculate the number of moles of
    ammonia present in a sample with a volume of
    12.0L, at 22.0oC and 715mmHg.

32
12.3 IDEAL GAS LAW
  • 5. Density of gas
  • PV mass RT mass P(M.M.) D
  • M.M. V RT

33
12.3 IDEAL GAS LAW
  • 6. Ex12.7 What is the density of oxygen gas at
    1.00 atm and 27.0oC?

34
12.3 IDEAL GAS LAW
  • 7. Calculating molar mass
  • PV mass RT
  • M.M.

35
12.3 IDEAL GAS LAW
  • 8. Ex12.8 What is the molar mass of a gas whose
    density is 5.00g/L at 25.0oC and 1.00atm?

36
12.4 GAS LAWS AND CHEMICAL REACTIONS
  • 1. Ex12.9 Hydrogen peroxide decomposes in the
    presence of sunlight to produce oxygen gas and
    water. Calculate the amount, in grams, of
    hydrogen peroxide needed to produce 2.50L of
    oxygen, measured at STP.

37
12.4 GAS LAWS AND CHEMICAL REACTIONS
  • 2. Ex12.10 How many liters of oxygen gas at
    1.00atm and 27.0oC are needed to burn 1.00g of
    octane (C8H18)?

38
12.4 GAS LAWS AND CHEMICAL REACTIONS
  • 3. Ex12.11 What mass in grams of potassium
    chlorate must be used to produce 1.75L of oxygen
    gas, measured at 18.0oC and 0.950atm according to
    the following equation?
  • 2KClO3(s) ? 3O2(g) 2KCl(s)

39
12.5 GAS MIXTURES AND PARTIAL PRESSURES
  • 1. Statement of Dalton's Law of Partial
    Pressures
  • Total pressure of a mixture of gases is equal to
    sum of the partial pressures of each component
  • Ptotal Pgas 1 Pgas 2 Pgas 3

40
12.5 GAS MIXTURES AND PARTIAL PRESSURES
  • 2. Ex12.12 A gas mixture has a total pressure
    of 1.50atm. If the mixture consists of 0.150mol
    of methane and an unknown amount of ethane in an
    8.50L vessel at 298K, what is the partial
    pressure due to ethane?

41
12.5 GAS MIXTURES AND PARTIAL PRESSURES
  • 3. Gases collected by bubbling through water and
    water vapor pressure
  • Collection over water? Ptotal Pgas PH2O
  • When level of gas level of water, pressures are
    equal
  • See. Pg. 13 in Reference Booklet

42
12.5 GAS MIXTURES AND PARTIAL PRESSURES
  • 4. Ex12.13 30.0mL of hydrogen gas is collected
    over water at a total pressure of 744mmHg and at
    20.0oC. Calculate the pressure due to hydrogen
    gas and the number of moles of hydrogen gas.

43
12.5 GAS MIXTURES AND PARTIAL PRESSURES
  • 5. Mole fractions
  • The ratio of the moles of a gas over the total
    moles of a gas in a mixture of ideal gases
  • Xa na
  • ntotal

44
12.5 GAS MIXTURES AND PARTIAL PRESSURES
  • 6. Relationship between partial pressure, mole
    fraction, and total pressure
  • Pa Xa
  • Ptotal

45
12.5 GAS MIXTURES AND PARTIAL PRESSURES
  • 7. Ex12.14 Calculate the mole fractions of
    hydrogen and water vapor in the previous problem.

46
12.6 KINETIC MOLECULAR THEORY OF GASES
  • 1. Basic statements of Kinetic Molecular Theory
  • a. Gases consist of particles whose separation
    is much greater than the size of the particles,
    themselves.
  • b. The particles of a gas are in constant,
    random, and rapid motion.
  • c. Gas particles constantly collide with one
    another and with the walls of their container,
    but they do so without loss of energy.
  • d. The average kinetic energy of a sample of gas
    particles is proportional to the absolute
    temperature of the gas. Therefore, all molecules
    of gas, regardless of their mass, have the same
    average kinetic energy at the same temperature.

47
12.6 KINETIC MOLECULAR THEORY OF GASES
  • 2. The kinetic energy of a single molecule
  • KE ½ mu2
  • u speed
  • Different molecules can have different speeds, so
    only applies to a single molecule
  • 3. The average kinetic energy of a sample of gas
    molecules depends on
  • Kelvin Temperature only

48
12.6 KINETIC MOLECULAR THEORY OF GASES
  • 4. The average kinetic energy of the molecules
    in a gas sample is related to average u2
  • KE ½ mu2
  • 5. The relationship between mass, average speed,
    and temperature is
  • ?u2 3RT (Maxwells Eqn)
  • M.M.

49
12.6 KINETIC MOLECULAR THEORY OF GASES
  • 6. Maxwell-Boltzmann Distribution
  • Distribution of speeds (KE) of molecules
  • Areas under curves are the same

50
12.6 KINETIC MOLECULAR THEORY OF GASES
  • 7. Ex12.15 Calculate the average velocity (rms
    speed) of an oxygen molecule at 25.0oC.

51
12.6 KINETIC MOLECULAR THEORY OF GASES
  • 8. Ex12.16 A professional tennis player can
    serve a tennis ball at 45m/sec. At what
    temperature will an oxygen molecule have the same
    average speed?

52
12.7 DIFFUSION AND EFFUSION
  • 1. Diffusion and Effusion
  • Diffusion mixing of gases due to molecular
    motion
  • Ex. Spread of aroma of a baking pie
  • Effusion movement of gas through a tiny opening
    in a container to another container of lower P
  • Ex. Punching a hole in a He balloon

53
12.7 DIFFUSION AND EFFUSION
  • 2. Graham's Law relating molar mass, rate of
    speed, and time
  • Rate of effusion of gas 1 M.M.-gas 2
  • Rate of effusion of gas 2 ?M.M.-gas 1
  • Rate of effusion of gas 1 rms for gas 1
    ? 3RT/(MM-gas 1)
  • Rate of effusion of gas 2 rms for gas 2
    ? 3RT/(MM-gas 2)

54
12.7 DIFFUSION AND EFFUSION
  • 3. Ex12.17 It takes 40sec for a sample of
    oxygen to effuse through a small opening into a
    vacuum. Another gas takes only 10sec to effuse
    under the same conditions. What is the molar
    mass of the second gas?

55
12.7 DIFFUSION AND EFFUSION
  • 4. Ex12.18 The ratio of the average rate of
    effusion of SO2(g) to CH4(g) at 300K is

56
12.8 NON-IDEAL BEHAVIOR REAL GASES
  • 1. Equations used to describe ideal gases are
    based on assumptions of kinetic molecular theory.
  • Gases actually have a volume
  • 1L container does not mean gas molecules have 1L
    to move about
  • Elastic Collisions are not always observed
  • When we approach the condensation point?
    molecules MUST have some attraction

57
12.8 NON-IDEAL BEHAVIOR REAL GASES
  • 2. Real gases deviate from ideal behavior under
    two main conditions
  • Low Temperature (approaching condensation)
  • High Pressure (molecular volume becomes
    significant)

58
12.8 NON-IDEAL BEHAVIOR REAL GASES
  • 3. van der Waal's Equation - a better predictor
    of gas behavior under extreme conditions
  • Corrects for intermolecular forces and molecular
    volume
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