Introduction to Gas Laws

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Introduction to Gas Laws

• Honors Chemistry
• Chapter 13-14

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Phases of Matter (REVIEW)
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Phases and Their Properties (REVIEW)

• Solid
• Liquid
• Gas
• Movement at the molecular level

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Phases and Their Properties (REVIEW)

• Solid

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Phases and Their Properties (REVIEW)

• Liquid

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Phases and Their Properties (REVIEW)

• Gas

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Properties of Liquids and the Kinetic-Molecular
Theory

• A liquid can be described as a form of matter
  that has a definite volume and takes the shape of
  its container.
• The attractive forces between particles in a
  liquid are more effective than those between
  particles in a gas.
• This attraction between liquid particles is
  caused by the intermolecular forces
• dipole-dipole forces
• London dispersion forces
• hydrogen bonding

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Properties of Liquids and the Kinetic-Molecular
Theory, continued

• The particles in a liquid are not bound together
  in fixed positions. Instead, they move about
  constantly.
• A fluid is a substance that can flow and
  therefore take the shape of its container.
• 1- Relatively High Density
• At normal atmospheric pressure, most substances
  are hundreds of times denser in a liquid state
  than in a gaseous state.

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Properties of Liquids and the Kinetic-Molecular
Theory, continued

• 2 - Relative Incompressibility
• Liquids are much less compressible than gases
  because liquid particles are more closely packed
  together.
• 3 - Ability to Diffuse
• Any liquid gradually diffuses throughout any
  other liquid in which it can dissolve.
• The constant, random motion of particles causes
  diffusion in liquids.
• As the temperature of a liquid is increased,
  diffusion occurs more rapidly.

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Diffusion
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Properties of Liquids and the Kinetic-Molecular
Theory, continued

• 4 - Surface Tension
• A property common to all liquids is surface
  tension, a force that tends to pull adjacent
  parts of a liquids surface together, thereby
  decreasing surface area to the smallest possible
  size.
• Capillary action is the attraction of the surface
  of a liquid to the surface of a solid.
• This attraction tends to pull the liquid
  molecules upward along the surface and against
  the pull of gravity.

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Properties of Liquids and the Kinetic-Molecular
Theory, continued

• 5 - Viscosity
• Fluidity is the ability to flow, which gases and
  liquids have. Viscosity is a measure of a
  liquids resistance to flow.
• This is determined by the type of intermolecular
  forces in a liquid.
• As temperature increases, viscosity decreases.
  The molecules increase in average kinetic energy
  and flow easier.

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Nature of gases(as explained by
kinetic-molecular theory)

• Gas consists of small particles that have mass

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Nature of gases(as explained by
kinetic-molecular theory)

• Gas consists of small particles that have mass
• Particles easily compressed
• (lots of space between the particles)

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Nature of gases(as explained by
kinetic-molecular theory)

• Gas consists of small particles that have mass
• Particles easily compressed
• (lots of space between the particles)
• Particles in constant, random motion
• occupy the volume of their container
• diffuse easily throughout each other

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Nature of gases(as explained by
kinetic-molecular theory)

• Gas consists of small particles that have mass
• Particles easily compressed
• (lots of space between the particles)
• Particles in constant, random motion
• occupy the volume of their container
• diffuse easily throughout each other
• Particles exert pressure
• gas pressure due to particles striking sides
  of container
• collisions of particles are elastic

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Nature of gases(as explained by
kinetic-molecular theory)

• Gas consists of small particles that have mass
• Particles easily compressed
• (lots of space between the particles)
• Particles in constant, random motion
• occupy the volume of their container
• diffuse easily throughout each other
• Particles exert pressure
• gas pressure due to particles striking sides
  of container
• collisions of particles are elastic
• Greatly affected by temperature
• particles speed up at higher temps exert
  higher press

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Measurements of Gases involve 4 variables

• Amount of gas (n) (number of moles)

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Measurements of Gases involve 4 variables

• Amount of gas (n) (number of moles)
• Volume (V)

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Measurements of Gases involve 4 variables

• Amount of gas (n) (number of moles)
• Volume (V)
• Temperature (T)
• measurements MUST be in Kelvin

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How To Convert Celsius to Kelvin

• To change from Celsius to Kelvin add 273 to the
  C
• Example 10C 283 K (no sign on the Kelvin
  temp)
• Example 302 K 29C
• Practice 47C ? K
• 21C ? K
• ? C 355 K
• ? C 261 K

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Measurements of Gases involve 4 variables

• Amount of gas (n) (number of moles)
• Volume (V)
• Temperature (T)
• measurements MUST be in Kelvin
• Pressure (P)

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Measurements of Gases involve 4 variables

• Amount of gas (n)
• Volume (V) measured in Liters
• Temperature (T)
• measurements MUST be in Kelvin
• Pressure (P)
• measured in kPa, OR
• atmospheres, OR
• millimeters of Hg

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Practice

• We can easily convert from one
• pressure unit to another because
• we know values that are equivalent
• 101.3 kPa 1 atmosphere (atm) 760 mm Hg
• Example 120 kPa x 760 mm Hg 900.3 mm Hg
• 101.3 kPa
• Example 727 mm Hg x 1 atm 0.96
  atm
• 760 mm Hg
• Example 1.29 atm ? mm Hg

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Balanced Equations tell us the following
information about gases

• Relative number of particles

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Balanced Equations tell us the following
information about gases

• Relative number of particles
• Relative number of moles

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Balanced Equations tell us the following
information about gases

• Relative number of particles
• Relative number of moles
• Relative volume of gases

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Balanced Equations tell us the following
information about gases

• Relative number of particles
• Relative number of moles
• Relative volume of gases
• 1 mole of gas 22.4 L of gas (AT STP)
• Hhhmm.What is STP?
• From the coefficients

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Atmospheric Pressure

• Pressure exerted by the air in the atmosphere
• Due to mass of air above object force of
  gravity
• Standard is set at average atmospheric pressure
  at sea level
• 101.3 kPa 1 atmosphere 760 mm Hg
• Atmospheric pressure varies with altitude
• (higher altitudes lower atmospheric
  pressure)
• Barometer measures atmospheric pressure
• dropping barometric reading means water vapor
  content of air is increasing (rain coming)

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Barometer
Atmospheric pressure
vacuum
Column of mercury
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Atmospheric Pressure

• Pressure exerted by the air in the atmosphere
• Due to mass of air above object force of
  gravity
• Standard is set at average atmospheric pressure
  at sea level
• 101.3 kPa 1 atmosphere 760 mm Hg
• Atmospheric pressure varies with altitude
• (higher altitudes lower atmospheric
  pressure)
• Barometer measures atmospheric pressure
• dropping barometric reading means water vapor
  content of air is increasing (rain coming)
• Manometer measures gas pressure in sealed
  container

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Standard Temperature Pressure(STP)for Ideal
Gases

• Temperature 0C
• Pressure 1 atmosphere 760 mm Hg 101.3 kPa
• 1 mole 22.4 Liters

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Back to Liquids -- Boiling

• A liquid boils when the vapor pressure the
  external pressure (atmospheric)
• Normal Boiling point is the temperature a
  substance boils at 1 atm pressure.
• The temperature of a liquid can never rise above
  its boiling point. Why?

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Changing the Boiling Point

• Lower the external atmospheric pressure (going up
  into the mountains).
• Lower external pressure then requires lower vapor
  pressure.
• Lower vapor pressure means lower boiling point.
• Boiling food cooks slower.

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Changing the Boiling Point

• Raise the external pressure (Use a pressure
  cooker).
• Raises the vapor pressure needed.
• Raises the boiling point.
• Boiling food cooks faster at the higher water
  temperature.

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Freezing
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ATTRACTIVE FORCES
electrostatic in nature
Intramolecular forces
bonding forces
These forces exist within each molecule. They
influence the chemical properties of the
substance.
Intermolecular forces
nonbonding forces
These forces exist between molecules. They
influence the physical properties of the
substance.
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Phase Changes
sublimation
vaporizing
melting
solid
liquid
gas
condensing
freezing
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Table 12.1
A Macroscopic Comparison of Gases, Liquids, and
Solids
State
Shape and Volume
Compressibility
Ability to Flow
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Energy and Phase Change

• Heat of vaporization energy required to change
  one gram of a substance from liquid to gas.
• Heat of condensation energy released when one
  gram of a substance changes from gas to liquid.
• For water 540 cal/g

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Energy and Phase Change

• Heat of fusion energy required to change one gram
  of a substance from solid to liquid.
• Heat of solidification energy released when one
  gram of a substance changes from liquid to solid.
• For water 80 cal/g

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Who Uses Gas Laws?

• Hot Air Balloonists

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Who Uses Gas Laws?

• Scuba Divers

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Who Uses Gas Laws?

• Factories that Bottle Soda

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Who Uses Gas Laws?

• Bicyclists