Gas Laws Chapter 14

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Gas LawsChapter 14
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Properties of Gases

• Gases are easily compressed because of the space
  between the particles in the gas.

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Properties of Gases

• The amount of gas, volume, and temperature affect
  the pressure of a gas.

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Properties of Gases

• Doubling the number of particles in the container
  would double the pressure on a contained gas at
  constant temperature.
• Boyles Law P1V1 P2V2

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• A) 50 kPa
• B) 33 kPa
• C) inverse proportion - as one increases the
  other decreases

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• Reducing the volume of a contained gas to one
  third, while holding temperature constant, causes
  pressure to become tripled.

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• A gas occupies a volume of 2.50 L at a pressure
  of 350.0 kPa. If the temperature remains
  constant, what volume would the gas occupy at
  1750 kPa?
• V V2 ? V1 2.50 L P1 350.0 kPa
• P2 1750 kPa
• F P1V1 P2V2
• S (350.0 kPa)(2.50 L) (1750 kPa)V2
• A V2 0.500 L

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• Boyles Law Temperature 14B

• If the volume of a container of gas is reduced,
  the pressure inside the container will increase.

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• The graph of several pressure-volume readings on
  a contained gas at constant temperature would be
  a curved line.

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• If a balloon is squeezed, the pressure of the gas
  inside the balloon increases.

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• Temperature is directly proportional to the
  average kinetic energy of the particles in a
  substance.

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• As the temperature of the gas in a balloon
  decreases, the average kinetic energy of the gas
  decreases.

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• Absolute zero is the temperature at which the
  average kinetic energy of particles would
  theoretically be zero.
• This is the lowest possible temperature.
  (-273.15C)

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• To get kelvins add 273 to the C.
• To get C subtract 273 from the kelvins.

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• A temperature of -25C is equivalent to 248 K.
  -25273248
• A temperature of 295 K is equivalent to 22 C.
  295-27322C

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• When the Kelvin temperature of an enclosed gas
  doubles, the particles of the gas move faster.
• The Kelvin temperature must be used when working
  with proportions.

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• Problem
• A balloon contains 30.0 L of helium gas at 103
  kPa. What is the volume of the helium when the
  balloon rises to an altitude where the
  temperature stays the same but the pressure is
  only 25.0 kPa?

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• V V2 ?
• P1 103 kPa V1 30.0 L
• P2 25.0 kPa V2 ?
• F P1V1 P2V2
• S (103 kPa)(30.0 L) (25.0 kPa)V2
• A V2 124 L

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Charles Law
Notes 14C

• when the temperature is
  expressed in kelvins.

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• At constant pressure, the volume of a fixed mass
  of gas and its Kelvin temperature are said to be
  directly related.

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• If a balloon is heated, the volume of the air in
  the balloon increases if the pressure is constant.

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• The temperature of 6.24 L of a gas is increased
  from 125 K to 250 k at constant pressure. What
  is the new volume of the gas?

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• V V2 ? V1 6.24 L
• T1 125 K T2 250. K
• F
• S
• A V2 12.48 L

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• A) kelvins B) increases C) 0 L

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Combined Gas Law
Notes 14 D

• Gay-Lussacs Law

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• If the Kelvin temperature of a gas in a closed
  container increases the pressure of the gas
  increases proportionally.

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• As the temperature of a fixed volume of a gas
  increases, the pressure will increase.

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• A sample of chlorine gas has a pressure of 9.99
  kPa at 27C. What will its pressure be at 627C
  if its volume remains constant?

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• V P2 ? P1 9.99 kPa
• T1 300. K T2 900. K
• F
• S
• A P2 29.97 kPa

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• The Combined Gas Law

The combined gas law relates temperature,
pressure, and volume.
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• If a sample of oxygen occupies a volume of 6.00 L
  at a pressure of 68.0 kPa and a temperature of
  264 K, what volume would this sample occupy at
  204 kPa and 528 K?

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• V V2 ? V1 6.00 L
• P1 68.0 kPa T1 264 K
• P2 204 kPa T2 528 K
• F
• S
• A V2 4.00 L

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Ideal Gas Law
Notes 14E

• Ideal Gas Law PV nRT
• Where n the number of moles
• R is the Ideal Gas Constant
• The ideal gas law can be used to calculate the
  number of moles of a contained gas.

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• What is the volume (in L) that would be occupied
  by 1.00 mol of O2 at STP?
• V V ? n 1.00 mol T 273K
• P 101.3 kPa
• F PV nRT
• S (101.3 kPa)V (1.00 mol)
  (273 K)
• A Vol 22.4 L

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• How many moles of H2 would be contained in 83.1 L
  of the gas at 137 kPa and 1.0C?

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• V n ? V 83.1 L P 137 kPa
  T 1.0C 274 K
• F PV nRT
• S (137 kPa)(83.1 L) n (274. K)
• A n 5.00 mol

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Gas Mixtures
14 F

• Daltons Law - In a mixture of gases, the total
  pressure is the sum of the partial pressures of
  the gases.
• PTotal P1 P2 P3

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• A sample of H2 is collected over water such that
  the combined hydrogen-water vapor sample is held
  at a pressure of 1 standard atmosphere. What is
  the partial pressure of the H2 if that of the
  water vapor is 2.5 kPa?
• 1 atm 101.3 kPa
• 101.3 kPa 2.5 kPa 98.8 kPa

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• The tendency of molecules to move toward areas of
  lower concentration is called diffusion.
• The gas propellant in an aerosol can moves from a
  region of high pressure to a region of lower
  pressure.

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• The process that occurs when a gas escapes
  through a tiny hole in the container is called
  effusion.
• The substance with the smallest molar mass would
  have the fastest rate of effusion.
• So CH4 effuses faster than NO2.
• 16g/mol 46g/mol

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