Chemistry - Gas Laws
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Chemistry - Gas Laws






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Chemistry - Gas Laws Chemistry - Gas Laws Presentation Transcript

  • Gases: Behavior and Calculations Chapter 14 or Chapter 12
  • Make two lists of equal size.
    • What I know about gases from chemistry class
    • What I know about gases from outside of chemistry class
  • Compare contrast a basketball shot with an over-inflated ball and a flat ball.
  • What would happen if your airbag was filled with liquid instead? Solid?
  • Changes in a Gas
    • What factor explains why SCUBA divers can carry all the oxygen they need in a small tank?
  • Review Questions
    • What is pressure?
    • How are the atoms/molecules in a gas arranged (compared to a liquid/solid)?
    • Define temperature.
  • Pressure
    • Pressure = force per unit area
  • Gases and Kinetic Theory
    • Molecules in constant, rapid, random motion
    • No forces exist between molecules
    • Temperature is a measure of molecular kinetic energy.
    • More molecules colliding with the container = more pressure
  • What affects pressure?
  • Variables
    • P (pressure) measures in kilopascals (kPa)
    • V (volume) measured in liters (L)
    • T (temperature) measured in Kelvins (K)
    • n (number of moles)
  • Kelvin Scale
    • Temperature in o C
    • + 273
    • = Temperature in K
  • Kelvin Scale
    • 60 o C = ?
    • 28 o C = ?
    • -6 o C = ?
    • 310 K = ?
    • 271 K = ?
  • Animated Gas Lab
  • Mathematical Relationships
    • Inverse Relationship:
      • One value goes down while the other goes up
    • Direct Relationship:
      • Both values change in the same direction
  • Boyle’s Law
    • If the volume of gas is lowered, how is the pressure affected? (Temperature held constant.)
  • Boyle’s Law
    • Pressure and volume share an inverse relationship, thus…
    • P 1 V 1 = P 2 V 2
  • Boyle’s Law
    • Nitrous oxide (N 2 O) is used as an anesthetic. The pressure on 2.50 L of N 2 O changes from 105 kPa to 40.5 kPa. If the temperature does not change, what will the new volume be?
  • Boyle’s Law
    • Carbon dioxide gas is contained within a balloon at a pressure of 160 kPa. If the balloon’s volume is suddenly decreased from 0.50 L to 0.20 L, will the pressure increase or decrease? What will the new pressure be? (Temperature remains constant.)
  • Boyle’s Law
    • You have volunteered to decorate the gym with helium balloons for a party. You find a store that will rent a 25-L helium tank filled with helium gas at a pressure of 3,040 kPa. You need to fill all 750 balloons with 1 liter of helium at a pressure of 106 kPa. Will one tank be enough to fill all the balloons?
  • Charles’ Law
    • If the temperature of a gas is lowered, how is the volume affected? (Pressure held constant.)
  • Charles’ Law
    • Volume and temperature share a direct relationship, thus…
    • V 1 V 2
    • ---- = ----
    • T 1 T 2
  • Charles’ Law
    • Exactly 5.00 L of air at 50 o C is warmed to 100 o C. What is the new volume if the pressure remains constant?
  • Charles’ Law
    • A SCUBA diver has a 1.50 L tank at a temperature of 25 o C. In order to maintain the same pressure, what temperature would a 1.35 L tank need to be stored at?
  • Charles’ Law
    • On a cool morning, (10.0 o C), a group of hot air balloonists fill their balloons with air. They fill their balloon to ¾ the volume, (1,275,000 L). At what temperature Celsius will the balloon completely fill with air (1,700,000 L) if the pressure and amount of gas remain constant?
  • Charles’ Law
    • If a sample of gas occupies 6.80 L at 325 o C, what will be its volume at 25 o C if the pressure does not change?
  • Charles’ Law
    • A perfectly spherical balloon with a radius of 16.0 cm is placed into a freezer. The freezer’s temperature is -7 o C while the temperature of the air outside the freezer is 31 o C. Calculate the new volume of the cooler balloon in LITERS.
    • Volume of a sphere = ( 4 / 3 ) π r 3
    • 1 cm 3 = 1 mL
  • Gay-Lussac’s Law
    • If the temperature of a gas is lowered, what happens to the pressure? (Volume is held constant.)
  • Gay-Lussac’s Law
    • Pressure and temperature share a direct relationship, thus…
    • P 1 P 2
    • ---- = ----
    • T 1 T 2
  • Gay-Lussac’s Law
    • Aerosol cans carry warning labels that say not to incinerate (burn) them or store them above a certain temperature. Why? The gas used in an aerosol can is at a pressure of 103 kPa at 25 o C. If the can is thrown in a fire and the temperature reaches 928 o C, what will the new pressure be?
  • Which Law?
    • A plastic container of nitrogen is placed into a freezer. If the volume of the container is 1.50 L at 20 o C, what will the volume be after the temperature drops to –2 o C?
  • Which Law?
    • A sample of neon has a pressure of 16.8 kPa at 489 K. If the volume does not change, what will the pressure be at 210 K?
  • Which Law?
    • If the pressure of a 5.0 L of a gas changes from 125 kPa to 700 kPa, what happens to the volume?
    • A sample of hydrogen gas has a volume of 56.0 L at 25 o C. If the volume rises to 65.0 L, at what temperature is the gas now?
  • Gas Laws
    • Boyle’s Law: PRESSURE and VOLUME are inversely proportional
    • Charles’ Law: VOLUME and TEMPERATURE are directly proportional
    • Guy-Lussac’s Law: PRESSURE and TEMPERATURE are directly proportional
  • Combined Gas Law
    • Can be used if none of the three variables (P, V, and T) remain constant.
    • P 1 V 1 P 2 V 2
    • -------- = --------
    • T 1 T 2
  • Combined Gas Law
    • A 2.50 liter balloon is filled with argon. The balloon has a pressure of 118 kPa at room temperature, 25 o C. If the balloon is put into a freezer (temperature of -6 o C) and its volume drops to 2.35 L, what is its new pressure?
  • Combined Gas Law
    • The volume of a gas-filled balloon is 30.0 L at 313 K and 153 kPa. What would the volume be at standard temperature and pressure?
  • Combined Gas Law
    • If the temperature and pressure of 4.0 liters of argon gas are changed from 65°C to 85°C and 150 kPa to 91 kPa respectively, calculate the change in the volume of the gas.
  • Use The Combined Gas Law…
    • On a warm May day (80 o F or 27 o C), a scuba diver on a boat takes 18.0 liters of air from a storage tank (stored at a relatively low pressure of 140 kPa) and transfers it to a small (7-liter) tank. When he jumps into the water, the pressure gauge on the tank reads 341 kPa. What temperature ( o C) is the ocean?
  • Ideal Gases
    • Besides volume, temperature, and pressure… what can we change about the gas in the balloon?
  • Moles of a Gas
    • 1.0 moles of a gas (at STP) takes up 22.4 L.
    • How does increasing the number of moles affect the volume of gas?
    • Direct or inverse relationship?
  • Moles of a Gas
    • Moles / Volume is directly proportional.
    • Moles ( n ) can now be added to the combined gas law!
  • Calculate the CONSTANT @ STP
    • P =
    • T =
    • V =
    • n =
  • CONSTANT ( R ) 8.3 L x kPa / K x mol
  • Ideal Gas Law
    • Contains pressure, volume, moles, temperature (in K) and the constant that relates the 4 quantities.
    • P x V
    • n = ---------- or PV = nRT
    • R x T
  • Example 1
    • A deep underground cavern contains 40,000 liters of space filled with methane gas, CH 4 . The gas is at a pressure of 150 kPa and a temperature of 40 o C. How many moles of CH 4 does the cavern contain?
  • Example 1, part 2
    • How many grams of CH 4 does the cavern contain?
  • Real Gases
    • Do not conform exactly to the ratio PV = nRT
    • (Very close around “normal” temperatures and pressures.)
    • Real gases differ most from an ideal gas at low temperatures and high pressures… WHY?
  • Real Gases
    • What happens to a gas at an extremely low temperature?
    • What happens to gases at extremely high pressures?
  • Example 2
    • What is the volume occupied by 0.900 mol of C 2 H 2 at room temperature at sea level (101 kPa and 27 o C)?
  • Example 3
    • How large would a container have to be to hold 3000 g of propane gas (C 3 H 8 ) if the gas was stored at 25 o C and a pressure of 500 kPa?
  • Example 4
    • A 50.00 liter tank at -15°C contains 14.00 grams of helium gas.
    • At what pressure is the gas within the tank?
  • Examples 5 and 6
    • Determine the number of moles of Krypton contained in a 3.25 liter gas tank at 540 kPa and 28°C. How many grams of Krypton are in the tank?
    • If the gas is Oxygen instead of Krypton, will the answer be the same in moles? In grams? Why or why not?
  • Fill in using Ideal Gas Law. Gas Argon Nitrogen Krypton Pressure 0.96 kPa --- 252 kPa Volume --- 5250 mL 465 L Temperature 200 o C 373 K --- Moles --- 0.0857 mol 25.0 mol Mass 12.5 g --- ---
  • Density
    • Calculate the density (g/m 3 ) of the following gases at standard temperature and pressure:
    • Hydrogen, Oxygen, Chlorine, Radon
    • 1 m 3 = 1000 L