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Chapters 10 and 11


... of 1 mm Hg is also called 1 torr in honor of Torricelli for his invention of the ... b. torr. c. kilopascals (kPa) Dalton's law of partial pressures ... – PowerPoint PPT presentation

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Title: Chapters 10 and 11

Chapters 10 and 11
HTC Modern Chemistry
  • Kinetic Molecular Theory
  • and
  • Gas Laws

The kinetic-molecular theory is based on the idea
that particles of matter are always in motion.
  • An ideal gas is a hypothetical gas that perfectly
    fits all the assumptions of the kinetic-molecular
  • A real gas does not behave completely according
    to the assumptions of the KMT. Highly polar
    gases, or those under high pressure at low
    temperature, are more likely to behave as a
    non-ideal gas.
  • Most gases behave ideally under normal conditions

The kinetic-molecular theory of gases is based on
the following five assumptions
  • Gases consist of large numbers of tiny particles
    that are far apart relative to their size.
  • Collisions between gas particles and between
    particles and container walls are elastic
  • Gas particles are in continuous, rapid, random
  • There are no forces of attraction (or repulsion)
    between gas particles.
  • The temperature of a gas depends on the average
    kinetic energy of the particles of the gas.

Properties of Gases
  • Expansion
  • Fluidity
  • Low density
  • Compressibility
  • Diffusion
  • Effusion

Properties of Liquids and the Kinetic-Molecular
  • The attractive forces between particles in a
    liquid are more effective than those between
    particles in a gas.
  • The particles in a liquid move about constantly.
  • A fluid is a substance that can flow and
    therefore take the shape of its container.

Properties of Liquids
  • Definite volume
  • Assumes shape of container
  • Relatively high density
  • Relative incompressibility
  • Ability to diffuse
  • Surface tension
  • Evaporation

Properties of Solids and the Kinetic-Molecular
  • The particles of a solid are more closely packed
    than those of a liquid or gas.
  • All inter-particle attractions exert stronger
    effects in solids than in the corresponding
    liquids or gases.
  • Attractive forces tend to hold the particles of a
    solid in relatively fixed positions.
  • Solids are more ordered than liquids and are much
    more ordered than gases.

Properties of Solids
  • Definite shape and volume
  • Definite melting point
  • High density
  • Incompressibility
  • Low rate of diffusion

There are two types of solids crystalline solids
and amorphous solids.
  • Most solids are crystalline solidsthey consist
    of crystals.
  • A crystal is a substance in which the particles
    are arranged in an orderly, geometric, repeating
  • An amorphous solid is one in which the particles
    are arranged randomly, such as glass and

Types of Crystalline Solids
  • Ionic crystals
  • and ions arranged in a regular pattern
  • Covalent network crystals
  • 3 dimensional covalently bonded structures such
    as quartz, diamond, and graphite
  • Metallic crystals
  • Metal cations surrounded by delocalized valence
  • Covalent molecular crystals
  • Covalently bonded compounds such as CO2, H2O, NH3

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Pressure (P) is defined as the force per unit
area on a surface.
  • Gas pressure is caused by collisions of the gas
    molecules with each other and with surfaces with
    which they come into contact.
  • The pressure exerted by a gas depends on volume,
    temperature, and the number of molecules present.
  • The greater the number of collisions of gas
    molecules, the higher the pressure will be.

Pressure is force per unit area.
  • The greater the force on a given area, the
    greater the pressure.
  • The smaller the area is on which a given force
    acts, the greater the pressure.

A barometer is a device used to measure
atmospheric pressure. The first barometer was
introduced by Evangelista Torricelli in the early
  • He sealed a long glass tube at one end and filled
    it with mercury. Inverting the tube into a dish
    of mercury, the mercury rose to a height of 760

Units of Pressure
  • The common unit of pressure is millimeters of
    mercury, symbolized mm Hg.
  • A pressure of 1 mm Hg is also called 1 torr in
    honor of Torricelli for his invention of the
  • Pressures can also be measured in atmospheres.
    Because the average atmospheric pressure at sea
    level at 0C is 760 mm Hg. 1 atm is defined as
    being exactly equivalent to 760 mm Hg.
  • In SI, pressure is expressed in pascals or
    kilopascals (kPa). 1 atm is equal to
    101.325 kPa

Converting Pressure
  • The average atmospheric pressure in Denver,
    Colorado is 0.830 atm. Express this pressure in
  • a. millimeters of mercury (mm Hg)
  • b. torr
  • c. kilopascals (kPa)

Daltons law of partial pressures
  • The pressure of each gas in a mixture is called
    the partial pressure of that gas.
  • John Dalton, the English chemist who proposed the
    atomic theory, discovered that the pressure
    exerted by each gas in a mixture is independent
    of that exerted by other gases present.
  • Daltons law of partial pressures states that the
    total pressure of a gas mixture is the sum of the
    partial pressures of the component gases.
  • Ptotal P1 P2 P3 . . .

Using Daltons Law
  • Oxygen gas from the decomposition of potassium
    chlorate, KClO3, was collected by water
    displacement. The barometric pressure and the
    temperature during the experiment were 731.0 torr
    and 20.0C. respectively. What was the partial
    pressure of the oxygen collected?
  • Patm Pgas Pwater

Robert Boyle discovered that doubling the
pressure on a sample of gas at constant
temperature reduces its volume by one-half.
  • This is explained by the kinetic-molecular
  • The pressure of a gas is caused by moving
    molecules hitting the container walls.
  • If the volume of a gas is decreased, more
    collisions will occur, and the pressure will
  • Likewise, if the volume of a gas is increased,
    fewer collisions will occur, and the pressure
    will decrease.

Boyles Law states that the volume of a fixed
mass of gas varies inversely with the pressure at
constant temperature.
  • Plotting the values of volume versus pressure for
    a gas at constant temperature gives a curve like
    that shown at right.
  • P1V1 P2V2

Applying Boyles Law
  • A sample of oxygen gas has a volume of 150.0 mL
    when its pressure is 0.947 atm. What will the
    volume of the gas be at a pressure of 0.987 atm
    if the temperature remains constant?

The quantitative relationship between volume and
temperature was discovered by the French
scientist Jacques Charles.
  • If pressure is constant, gases expand when
  • When the temperature increases, the volume of a
    fixed number of gas molecules must increase if
    the pressure is to stay constant.
  • At higher temperature, gas molecules move faster.
    They collide with the walls of the container more
    frequently and with more force.
  • The volume of a flexible container must then
    increase in order for the pressure to remain the

Charless law states that the volume of a fixed
mass of gas at constant pressure varies directly
with the Kelvin temperature.
  • Gas volume and Kelvin temperature are directly
    proportional to each other at constant pressure,
    as shown at right.

Applying Charless Law
  • A sample of neon gas occupies a volume of 752 mL
    at 25C. What volume will the gas occupy at 50C
    if the pressure remains constant?

The combined gas law expresses the relationship
between pressure, volume, and temperature of a
fixed amount of gas.
  • This single equation can be used for situations
    in which temperature, pressure, and volume, all
    vary at the same time.

  • A helium-filled balloon has a volume of 50.0 L at
    25C and 1.08 atm. What volume will it have at
    0.855 atm and 10.0C?

Gay-Lussacs Law
The quiz is next . . .
Multiple Choice
1. The SI unit of pressure is the A. atm B.
torr C. pascal D. mm Hg
Multiple Choice
  • 2. A sample of oxygen gas has a volume of 150 mL
    when its pressure is 0.923 atm. If the pressure
    is increased to 0.987 atm and the temperature
    remains constant, what will the new volume be?
  • A. 140 mL
  • B. 160 mL
  • C. 200 mL
  • D. 240 mL

Multiple Choice
  • 3. A sample of gas in a closed container at a
    temperature of 100.0C and 3.0 atm is heated to
    300.0C. What is the pressure of the gas at the
    higher temperature?
  • A. 35 atm
  • B. 4.6 atm
  • C. 59 atm
  • D. 9.0 atm

Short Answer
  • 4. Give a molecular explanation for the
    observation that the pressure of a gas increases
    when the gas volume is decreased.

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The density of liquids varies
  • Back

Surface Tension
Sodium in three phases
Mercury in three phases
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