Chapter 12 The Behavior of Gases

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Chapter 12 The Behavior of Gases
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• If a gas is heated, as in a hot air balloon, then
  its volume will increase. A heater in the
  balloon's basket heats the air inside the balloon
  and blows hot air into the balloon. As the volume
  of gas increases, it fills the balloon. Soon the
  balloon is full of hot air. If the air continues
  to heat up, it expands and flows out of the hole
  in the bottom of the balloon.

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Hence a balloon filled with hot air contains
fewer air molecules than the same balloon
inflated to the same size with cool air. A hot
air balloon will therefore be less dense than a
balloon filled with cool air as a consequence of
the ideal gas law.
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Chapter 12 The Behavior of Gases

• The Properties of Gases
• Factors Affecting Gas Pressure
• The Gas Laws
• Ideal Gases
• Gas Molecules Mixtures and Movements

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Chapter 12.1 The Properties of Gases

• Kinetic Theory Revisited
• Variables That Describe a Gas

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Kinetic Theory Revisited

• What do you recall about the Kinetic Theory as it
  relates to gases from Chapter 10?

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Assumptions of the Kinetic Theory as applies to
Gases

• A gas is composed of molecules or atoms that have
  insignificant volume and are spread very far
  apart. In between is empty space. No attractive
  or repulsive forces exist.

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Assumptions of the Kinetic Theory as applies to
Gases

• 2) The particles in a gas move rapidly in
  constant random motion.
• Travel in straight paths.
• Change direction only when they collide.

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Assumptions of the Kinetic Theory as applies to
Gases

• 3) All collisions are perfectly elastic. Kinetic
  energy is transferred. It is never lost.

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Collision Theory

• http//www.kscience.co.uk/animations/collision.swf
  

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Variables That Describe a Gas

• Pressure (P) kilopascals
• Volume (V) liters
• Temperature (T) Kelvin's
• Number of moles (n)

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Chapter 12.2 Factors Affecting Gas Pressure

• Amount of a Gas
• Volume
• Temperature

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Amount of a Gas

• What happens when you pump up a bike tire?

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Amount of a Gas

• Increase the amount of gas ? the pressure
  increases
• Why?
• More particles More Collisions

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Amount of a Gas

• Gas moves from higher pressure to lower pressure

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Volume

• If you decrease the volume, pressure ?
• Increases
• If you increase the volume, pressure?
• Decreases

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Temperature

• If you increase the temperature of a gas, the
  pressure?
• Increases
• If you decrease the temperature of a gas, the
  pressure?
• Decreases

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Chapter 12.3The Gas Laws

• Boyles Law
• Charless Law
• Gay-Lussacs Law
• Combined Gas Law

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Boyles Law (1662)

• Pressure Volume Relationship
• Pressure increases, Volume decreases
• Boyles Law for a gas with a given mass at a
  constant temperature, the volume of the gas
  varies inversely with the pressure
• P1 x V1 P2 x V2

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Charless Law (1787)

• Temperature Volume Relationship
• Temperature increases, Volume increases
• Charless Law for a gas with a fixed mass at a
  constant pressure, the volume of the gas varies
  directly with the temperature
• V1 V2
• T1 T2

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Gay-Lussacs Law (1802)

• Temperature Pressure Relationship
• Temperature increases, Pressure increases
• Gay-Lussacs Law for a gas at a constant
  volume, the pressure of the gas varies directly
  with the temperature
• P1 P2
• T1 T2

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Combined Gas Law

• Combines all three laws
• P1 V1 P2 V2
• T1 T2

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Chapter 12.4

• Ideal Gas Law
• Ideal Gas Law and Kinetic Theory

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Ideal Gas Law

• P x V n x R x T (PVnRT)
• n number of moles
• R Ideal Gas Constant 8.31 L kPa
• K mol

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Ideal Gas Law

• You fill a rigid steel cylinder that has a volume
  of 20.0 L with nitrogen gas to a final pressure
  of 20,000 kPa at 28ºC. How many moles of nitrogen
  gas does the cylinder contain?
• P 20,000 kPa
• V 20.0 L
• n ?
• R 8.31 L kPa
• K mol
• T 28ºC

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Ideal Gas Law

• PV nRT
• Change temperature to Kelvin
• 28ºC 273 301K
• Solve for the unknown
• (20,000kPa)(20.0L) n (8.31 L kPa) (301K)
• K mol
• 160 mol N2(g) n

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Ideal Gas Law

• A deep underground cavern contains 2.24x106 L of
  methane gas at a pressure of 1.50x103 kPa and a
  temperature of 42ºC. How many kilograms of
  methane does this natural gas deposit contain?
• 2.05x104 kg CH4

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Ideal Gas Law and Kinetic Theory

• States gas has no volume
• This is not a true statement
• All gases have mass
• Most gases behave like ideal gases.

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