Gases

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Chapter 10

• Gases

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What is a gas?

• Phase of matter that has no definite shape or
  volume.
• Conforms to the shape and volume of container.

http//www.harcourtschool.com/activity/states_of_m
atter/
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Kinetic Molecular Theory

• A simple model applied to explain the properties
  of an ideal gas.
• The particles are so small compared with the
  distances between them that the volume of the
  individual particles can be assumed to be
  negligible.

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• Particles are in constant motion. The collisions
  of the particles with the walls of the container
  are the cause of the pressure exerted by the gas.

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• The particles are assumed to exert no forces on
  each other they are assumed neither to attract
  nor repel one another.

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• The average kinetic energy of a collection of gas
  particles is assumed to be directly proportional
  to the Kelvin temperature of the gas.
• Real Gases do not conform to these postulates.
• Have finite volumes and do exert forces on one
  another.

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Measureable Properties
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Pressure

• Force applied uniformly over a surface.
• Measured as force per unit area.
• Measured using many units
• SI unit Newtons/m2
• Standard Pressure1.00 atmospheres

1.00 atm 760.0 mm Hg 760.0 torr 101.325 kPa
101,325 Pa
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Temperature

• Measure of the kinetic energy of the molecules
  that make up a substance.
• Use the Kelvin Scale
• K 273.15 C
• Thermodynamic temperature scale
• Defines absolute zero
• 0 K-273.15C
• Temperature at which all molecular movement stops

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Conversions
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Standard Temperature Pressure

• STP
• Standard Temperature 0.00C273.15K
• Standard Pressure 1.00atm

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Gas Laws
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Boyles Law

• Robert Boyle, Irish chemist developed law in mid
  1600s
• Pressure and volume are inversely related when
  temperature is held constant

V ? 1/P
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Illustration of Boyles law.
P1V1P2V2
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As Pressure Increases, the Volume of SO2 Decreases
0.57L
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Charless Law

• Volume of a gas at constant pressure increase
  linearly with temperature.
• Volume is directly proportional to temperature
• V ? T

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Avogadros Law

• At constant temperature and pressure, the volume
  of a gas is directly proportional to the number
  of moles of gas.
• V ? n

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The relationship between volume V and number of
moles n. As the number of moles is increased from
1 to 2 (a to b), the volume doubles.
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Gay-Lussacs Law

• The pressure of a fixed amount of gas at fixed
  volume is directly proportional to its
  temperature in kelvins.
• P ? T

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Combined Gas

• Evaluates in temperature, pressure and volume.

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Daltons Law of Partial Pressures

• mixture of ideal gases, each gas has a partial
  pressure which is the pressure which the gas
  would have if it alone occupied the volume.
• The total pressure is equal to the sum of partial
  pressures.

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When two gases are present, the total pressure is
the sum of the partial pressures of the gases.
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Collecting Gas Over Water

• Water molecules are constantly escaping the
  liquid phase to become vapor.
• Extent is dependent on temperature
• The total pressure observed is equal to the sum
  of the individual gases and the vapor pressure of
  water.

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Ideal Gas Law

• Gases behave ideally at pressure at or lower than
  1.00atm and temperature of 0.00C.
• Ideal Gas Law allows us to assume ideal behavior
  for all gases.

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PVnRT

• PPressure
• VVolume in Liters
• nnumber of moles
• RUniversal Gas Constant
• 0.08206 L atm/mol K
• 62.4 L mmHg/mol K
• 8.314 L kPa/ mol K
• TTemperature in Kelvin

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Example

• What volume is occupied by 0.250mol of carbon
  dioxide at 25.0C and 371 torr?

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Example

• Thermal decomposition of KClO3 produces oxygen.
  The gas is collected over water at 22C with an
  observed pressure of 754 torr and a volume of
  0.650L. Calculate the partial pressure of oxygen
  the number of moles present. The vapor pressure
  of water at 22C is 21 torr.

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The Production of Oxygen by Thermal Decomposition
of KClO3
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