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Honors Chemistry, Chapter 10


A pressure of 1 mm of Hg is now called 1 torr in honor of Torricelli. ... The barometric pressure was 731 torr and the temperature was 20.0oC. ... – PowerPoint PPT presentation

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Title: Honors Chemistry, Chapter 10

Chapter 10 Physical Characteristics of Gases
Kinetic-Molecular Theory
  • Kinetic-molecular theory is based on the idea
    that particles of matter are always in motion.
  • Ideal Gas an imaginary gas that perfectly fits
    all the assumptions of the kinetic-molecular

Assumptions of Kinetic-Molecular Theory
  • 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
    collisions. An elastic collision is one in which
    there is no net loss of kinetic energy.
  • Gas particles are in continuous, rapid, random
    motion. They therefore posses kinetic energy,
    which is energy of motion.

Assumptions of Kinetic-Molecular Theory
  • There are no forces of attraction or repulsion
    between gas particles.
  • The average kinetic energy of gas particles
    depends on the temperature of the gas.
  • KE ½ mv2 where KE is kinetic energy
  • m is mass and
  • v is velocity

Nature of Gases
  • Expansion Gases have no definite shape or
    definite volume so they expand to fill the
    container. Gas particles move rapidly in all
    directions (assumption 3) without significant
    attraction or repulsion between them (assumption
  • Fluidity Because the attractive forces between
    gas particles are insignificant (assumption 4),
    gas particles glide easily past one another.

Nature of Gases
  • Low Density The density of a gas is about
    1/1000 the density of the same substance in the
    liquid or solid state.
  • Compressibility During compression, the gas
    particles, which are initially very far apart
    (assumption 1), are crowded closer together.
    Under the influence of pressure, the volume of a
    gas can be greatly decreased.

Nature of Gases
  • Diffusion Gases spread out and mix with one
    another, even without being stirred. This
    spontaneous mixing of particles of two substances
    caused by their random motion is called
  • Effusion is a process by which gas particles pass
    through a tiny opening. Rates of effusion of
    different gases are directly proportional to the
    velocities of their particles.

Real Gases
  • A real-gas is a gas that does not behave
    completely according to the assumptions of the
    kinetic-molecular theory.
  • Deviations from ideal-gas behavior usually occur
    at high pressures and/or low temperatures where
    the attractive forces between molecules begin to
    play a role.

Chapter 10, Section 1 Review
  • State the kinetic molecular theory of matter, and
    describe how it explains certain properties of
  • List the five assumptions of the
    kinetic-molecular theory of gases.
  • Define the terms ideal gas and real gas.

Chapter 10, Section 1 Review continued
  • Describe each of the following characteristic
    properties of gases expansion, density,
    fluidity, compressibility, diffusion, and
  • Describe the conditions under which a real gas
    deviates from ideal behavior.

Pressure and Force
  • Pressure (P) is defined as the force per unit
    area on a surface.
  • pressure force/area
  • The SI unit for force is the newton, abbreviated
    N. It is the force that will increase the speed
    of a one kilogram mass by 1 meter per second per
    second that it is applied.
  • force mass x acceleration

Example Pressure on the Feet of a Ballet Dancer
  • Acceleration of gravity is 9.8 m/s/s
  • What is the force of a 51 Kg dancer on the floor?
  • F m x a 51 kg x 9.8 m/s/s 500 N
  • What is the pressure?
  • Flat footed 500 N/325 cm2 1.5 N/cm2
  • Two feet tip toes 500 N /13 cm2 38.5
  • One foot tip toes 500 N /6.5 cm2 77 N/cm2

Units of Pressure
  • A common unit of pressure is millimeters of
    mercury, mm Hg. A pressure of 1 mm of Hg is now
    called 1 torr in honor of Torricelli.
  • One atmosphere is defined as being exactly
    equivalent to 760 mm Hg.
  • In SI units, pressure is expressed in derived
    units called pascals. One pascal (Pa) is defined
    as the pressure exerted by a force of one newton
    (1 N) acting on an area of 1 square meter. One
    atmosphere is 1.01325 x 105 Pa or 101.325 kPa.

Units of Pressure
Standard Temperature and Pressure
  • For purposes of comparison, scientists have
    agreed on standard conditions of exactly 1 atm
    pressure and 0oC. These conditions are called
    standard temperature and pressure and are
    commonly abbreviated STP.

Pressure Units Conversions
  • Convert 0.830 atm to mm of Hg and kPa
  • 0.830 atm x 760 mm of Hg/atm 631 mm
    of Hg
  • 0.830 atm x 101.325 kPa/atm
  • 84.1 kPa

Chapter 10, Section 2 Review
  • Define pressure and relate it to force.
  • Describe how pressure is measured.
  • Convert units of pressure.
  • State the standard conditions of temperature and

Gas Laws
  • Gas laws are simple mathematical relationships
    between the volume, temperature, pressure, and
    amount of a gas.
  • Boyles Law states that the volume of a fixed
    mass of gas varies inversely with the pressure at
    constant temperature.

Illustration of Boyles Law
Mathematical Expression of Boyles Law
  • V k/P or PV k
  • P1V1 k P2V2 k
  • P1V1 P2V2
  • P1V1 / V2 P2

Volume-Pressure Data
Boyles Law Example Problem
  • V 150. mL of O2 at 0.947 atm.
  • What is the volume at 0.987 atm (at constant
  • Formula P1V1 / P2 V2
  • 0.947 atm x 150. mL / 0.987 atm 144 mL of O2

Absolute Zero
  • Absolute zero, -273.15 oC., is the lowest
    temperature possible. This is assigned a value
    of zero on the Kelvin scale.
  • To convert from Celsius to Kelvin
  • K 273.15 oC.
  • To convert from Kelvin to Celsius
  • oC. K 273.15

Charless Law
  • Charless Law states that the volume of a fixed
    mass of gas at constant pressure varies directly
    with the Kelvin temperature.
  • V kT or V/T k
  • V1 / T1 V2 / T2

Plot of Volume vs. Temperature
Charless Law Example Problem
  • A sample of Ne gas has a volume of 752 mL at 25
    oC. What volume will the gas occupy at 50 oC. if
    the pressure remains constant?
  • Convert temperatures to Kelvin
  • 25 oC. 273 298 K.
  • 50 oC. 273 323 K.

Charless Law Sample Problem
  • V2 V1 x T2 / T1
  • V2 752 mL Ne x 323 K. / 298 K
  • 815 mL of Ne

Gay-Lussacs Law
  • Gay-Lussacs Law The pressure of a fixed mass of
    gas at constant volume varies directly with the
    Kelvin temperature.
  • P kT or P/T k
  • P1/T1 P2/T2

Gay-Lussacs Law Example Problem
  • Gas in an aerosol can is 3.00 atm at 25oC.
  • What is the pressure at 52oC.?
  • P2 P1 x T2/T1
  • Convert temperatures to Kelvin
  • 25oC. 273 298 K.
  • 52oC. 273 325 K.

Gay-Lussacs Law Example Problem
P2 3.00 atm x 325 K / 298 K 3.27 atm
Combined Gas Law
  • The combined gas law expresses the relationship
    between pressure, volume, and temperature of a
    fixed amount of gas.
  • PV/T k
  • Or
  • P1 V1/T1 P2 V2 / T2

Combined Gas Law Example Problem
  • A helium-filled balloon has a volume of 50.0 L at
    25 oC. and 1.08 atm. What volume will it have at
    0.855 atm and 10 oC.?
  • Convert the temperatures to Kelvin
  • 25 oC. 273 298 K
  • 10 oC. 273 283 K.
  • V2 P1 V1 T2 /( P2 T1)

Combined Gas Law Example Problem
V2 P1 V1 T2 /( P2 T1) V2 1.08 atm x50 L
Hex283 K/(0.855atm x298 K) 60.0 L
Daltons Law of Partial Pressures
  • Daltons law of partial pressures states that the
    total pressure of a mixture of gases is equal to
    the sum of the partial pressures of the component
  • PT P1 P2 P3

Partial Pressure Example
  • Oxygen gas is collected over water. The
    barometric pressure was 731 torr and the
    temperature was 20.0oC. What was the partial
    pressure of the oxygen collected?
  • PT 731 torr
  • Pwater 17.5 torr at 20.0oC.

Partial Pressure Example
Poxygen PT Pwater Poxygen 731
torr 17.5 torr 713.5 torr
Chapter 10, Section 3, Review
  • Use the kinetic-molecular theory to explain the
    relationship between gas volume, temperature, and
  • Use Boyles law to calculate volume-pressure
    changes at constant temperature.
  • Use Gay-Lussacs law to calculate
    pressure-temperature changes at constant volume.

Chapter 10, Section 3, Review continued
  • Use the combined gas law to calculate
    volume-temperature-pressure changes.
  • Use Daltons law of partial pressures to
    calculate the partial pressures and total
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