The Gas Laws!

1
The Gas Laws!

• Ch 14 Notes

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Properties of Gases

• Gases are compressible because of the space
  between particles.
• Factors that affect gases
• Pressure
• Volume
• Temperature
• of moles present

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Boyles Law

• P1V1 P2V2
• Inverse Relationship
• T is constant
• If one goes up, the other goes down
• If one goes down, the other goes up

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Lung model, marshmellows, bell jar, crush the can
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Boyles Law Sample Prob

• You and your crazy friend want to make funny
  voices using helium. You obtain a helium tank.
• The volume of the gas in the tank is 2 L, but can
  fill over 200 L at room pressure. Room pressure
  is 1 atm, what was the original pressure?

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Charless Law

• V1 V2
• T1 T2
• Direct Relationship
• P is constant and the amount of gas is constant
• Temperature in Kelvin !!! (C 273)
• As V increases, so does T
• As V decreases, so does T
• higher temp more kinetic energy, more
  collisions, so volume increases

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Charless Law Sample Prob

• The temperature in the supermarket is a frosty 15
  C. When you buy your bag of chips it occupies 1
  L of space. You leave the chips in your car for
  1 hour and it reaches a temperature of 27 C.
  what is the new volume of the bag?

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Gay-Lussacs Law

• P1/T1 P2/T2
• Direct Relationship
• Temp in Kelvin!!!
• Volume and amount of gas is constant
• Example The temperature of a gas goes from 30
  C to 50 C. The starting pressure is 760mmHg,
  what is the final pressure?

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Go To Absolute Zero Video Clip
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Combined Gas Law

• P1V1/T1 P2V2/T2
• Combines Boyles, Charles, and Gay-Lussacs Laws
• Sample Your mom gives you a balloon that says
  I love you! (awh!). When she hands it to you
  it has a pressure of 1.5 atm and is at 295 K.
  The next morning it is at 290 K, has a pressure
  of 1.2 atm and has a volume of 1.5 L. What was
  the original volume of the balloon?

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Molar Volume

• At STP, 1 mole of any gas occupies 22.4 L
• STP 0 C (273 K) and 1 atm
• What will be the volume of 5 moles of gas at STP?
• A sample of gas occupies 11.2 L at STP, how many
  moles is in the sample?
• How many grams of chlorine are in 5 L of chlorine
  gas at STP?

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Ideal Gas Law

• relates P, V, T, and the amount of gas in moles
  (n)
• PV nRT
• R ideal gas law constant
• There are many values for R -- choose the one
  that agrees with your pressure units.
• Volume must be in LITERS and temperature in
  KELVIN!
• ideal gases - particles have no volume, no
  attractive/repulsive forces, dont liquefy under
  high pressure or low temperature
• real gases are ideal gases under all conditions
  except very high pressure or very low temperature

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Sample Problems

1. You have 4 moles of helium gas at 1.5 atm and 25
   L, what is the temperature?
2. How many moles of argon gas are present in 500 mL
   at 3 atm and 30 ºC?

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Gas Stoichiometry

• Coefficients in balanced reaction equations are
  mole ratios AND gas volume ratios!
• Can do volume to volume stoichiometry when P
  and T are held constant

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Volume - Volume Gas Stoich

• (These are just like mole to mole
• problems - one conversion!)
• How many liters of NH3 will be produced if 10
  liters of N2 are consumed according to the
  following reaction
• N2 (g) 3H2 (g) -----gt 2NH3 (g)

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Volume-Mass Gas Stoich Example

• N2 (g) 3H2 (g) -----gt 2NH3 (g)
• How many grams of hydrogen gas are required to
  create 20L of ammonia gas if the above reaction
  occurs at STP?
• do volume to volume stoich, then molar volume,
  then molar mass.

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Mass-Volume Gas Stoich Example

• N2 (g) 3H2 (g) -----gt 2NH3 (g)
• How many liters of ammonia gas can be created
  from 50 grams of nitrogen gas at STP?
• mass to mole, mole ratio, then molar volume