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  • Gases: Behavior and CalculationsQBA Miguel A. Castro Ramírez
  • Make two lists of equal size.• What I know about • What I know about gases from chemistry gases from outside of class chemistry class
  • Compare contrast abasketball shot with an over-inflated ball and a flat ball.
  • What would happen if yourairbag was filled with liquidinstead? Solid?
  • Changes in a Gas • What factor explains why SCUBA divers can carry all the oxygen they need in a small tank?
  • Review Questions1. What is pressure?2. How are the atoms/molecules in a gas arranged (compared to a liquid/solid)?3. 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?1.2.3.
  • VariablesP (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 oC + 273 = Temperature in K• NOT DEGREES K!
  • Kelvin Scale • 60oC = ? • 28oC = ? • -6oC = ? • 310 K = ? • 271 K = ?
  • Animated Gas Lab• http://intro.chem.okstate.edu/1314F00/Laboratory
  • 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.) • http://www.grc.nasa.gov/WWW/
  • Boyle’s Law • Pressure and volume share an inverse relationship, thus… P1V1 = P2V2
  • Boyle’s Law• Nitrous oxide (N2O) is used as an anesthetic. The pressure on 2.50 L of N2O 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?
  • Boyle’s Law• The pressure on 2.50 L of anesthetic gas changes from 105 kPa to 40.5 kPa. What will be the new volume if the temperature remains constant?
  • 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… V1 V2 ---- = ---- T1 T2
  • Charles’ Law• Exactly 5.00 L of air at 50.0oC is warmed to 100.0oC. 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 25oC. 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, (10.0oC), 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 325oC, what will be its volume at 25oC if the pressure does not change?
  • 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… P1 P2 ---- = ---- T1 T2
  • 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 25oC. If the can is thrown in a fire and the temperature reaches 928oC, 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 20oC, what will the volume be after the temperature drops to –2oC?
  • 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 25oC. If the volume rises to 65.0 L, at what temperature is the gas now?
  • Which Law?• A sample of hydrogen gas has a volume of 56.0 L at 25oC. 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. P1V1 P2V2 -------- = -------- T1 T2
  • Combined Gas Law• A 2.50 liter balloon is filled with argon. The balloon has a pressure of 118 kPa at room temperature, 25oC. If the balloon is put into a freezer (temperature of -6oC) 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 (80oF or 27oC), 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 is the ocean?
  • Challenge Problem• Examine the following web page. Determine the pressure that the helium in a large tank is stored at if the tank is at room temperature and is 4 feet tall and eleven inches wide.http://www.arneswarehouse.com/heliumtank.htm
  • 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 @ STPP=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. PxV n = ---------- or PV = nRT RxT
  • Example 1• A deep underground cavern contains 2240 liters of space filled with methane gas, CH4. The gas is at a pressure of 150 kPa and a temperature of 40oC. How many moles of CH4 does the cavern contain?
  • Example 1, part 2• How many grams of CH4 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 C2H2 at STP?
  • Example 3• How large would a container have to be to hold 3000 g of propane gas (C3H8) if the gas was stored at 25oC and a pressure of 500 kPa?
  • Example 4 • A 50.00 liter tank at -15°C contains 14.00 grams of helium gas. How many moles of gas are in the tank? • At what pressure is the gas within the tank?
  • Examples 5 and 6• Determine the number of • At what moles of Krypton temperature will contained in a 3.25 liter 0.654 moles of gas tank at 540 kPa and neon gas 28°C. If the gas is Oxygen instead of occupy 12.30 Krypton, will the answer liters at 195 be the same? Why or kPa? why not?
  • Fill in using Ideal Gas Law. Gas Argon Nitrogen Krypton Pressure 0.96 kPa --- 252 kPa Volume --- 5.25 L 465 LTemperature 200oC 373 K --- Moles --- 0.0857 mol 25.0 mol Mass 12.5 g --- ---
  • Density• Calculate the density (g/m3) of the following gases at standard temperature and pressure:• Hydrogen, Oxygen, Chlorine, Radon• 1 liter = 0.001 cubic meters (m3)