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  1. 1. Gases: Behavior and CalculationsQBA Miguel A. Castro Ramírez
  2. 2. Make two lists of equal size.• What I know about • What I know about gases from chemistry gases from outside of class chemistry class
  3. 3. Compare contrast abasketball shot with an over-inflated ball and a flat ball.
  4. 4. What would happen if yourairbag was filled with liquidinstead? Solid?
  5. 5. Changes in a Gas • What factor explains why SCUBA divers can carry all the oxygen they need in a small tank?
  6. 6. Review Questions1. What is pressure?2. How are the atoms/molecules in a gas arranged (compared to a liquid/solid)?3. Define temperature.
  7. 7. Pressure• Pressure = force per unit area
  8. 8. 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
  9. 9. What affects pressure?1.2.3.
  10. 10. VariablesP (pressure) measures in kilopascals (kPa) V (volume) measured in liters (L)T (temperature) measured in Kelvins (K) n (number of moles)
  11. 11. Kelvin Scale• Temperature in oC + 273 = Temperature in K• NOT DEGREES K!
  12. 12. Kelvin Scale • 60oC = ? • 28oC = ? • -6oC = ? • 310 K = ? • 271 K = ?
  13. 13. Animated Gas Lab•
  14. 14. Mathematical Relationships• Inverse Relationship: – One value goes down while the other goes up• Direct Relationship: – Both values change in the same direction
  15. 15. Boyle’s Law • If the volume of gas is lowered, how is the pressure affected? (Temperature held constant.) •
  16. 16. Boyle’s Law • Pressure and volume share an inverse relationship, thus… P1V1 = P2V2
  17. 17. 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?
  18. 18. 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.)
  19. 19. 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?
  20. 20. 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?
  21. 21. Charles’ Law• If the temperature of a gas is lowered, how is the volume affected? (Pressure held constant.)
  22. 22. Charles’ Law• Volume and temperature share a direct relationship, thus… V1 V2 ---- = ---- T1 T2
  23. 23. 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?
  24. 24. 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?
  25. 25. 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?
  26. 26. 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?
  27. 27. Gay-Lussac’s Law • If the temperature of a gas is lowered, what happens to the pressure? (Volume is held constant.)
  28. 28. Gay-Lussac’s Law • Pressure and temperature share a direct relationship, thus… P1 P2 ---- = ---- T1 T2
  29. 29. 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?
  30. 30. 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?
  31. 31. 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?
  32. 32. 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?
  33. 33. 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?
  34. 34. 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
  35. 35. Combined Gas Law • Can be used if none of the three variables (P, V, and T) remain constant. P1V1 P2V2 -------- = -------- T1 T2
  36. 36. 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?
  37. 37. 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?
  38. 38. 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.
  39. 39. 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?
  40. 40. 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.
  41. 41. Ideal Gases
  42. 42. • Besides volume, temperature, and pressure… what can we change about the gas in the balloon?
  43. 43. 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?
  44. 44. Moles of a Gas• Moles / Volume is directly proportional.• Moles (n) can now be added to the combined gas law!
  45. 45. Calculate the CONSTANT @ STPP=T=V=n=
  46. 46. CONSTANT (R) 8.3 L x kPa / K x mol
  47. 47. Ideal Gas Law• Contains pressure, volume, moles, temperature (in K) and the constant that relates the 4 quantities. PxV n = ---------- or PV = nRT RxT
  48. 48. 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?
  49. 49. Example 1, part 2• How many grams of CH4 does the cavern contain?
  50. 50. 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?
  51. 51. Real Gases • What happens to a gas at an extremely low temperature? • What happens to gases at extremely high pressures?
  52. 52. Example 2• What is the volume occupied by 0.900 mol of C2H2 at STP?
  53. 53. 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?
  54. 54. 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?
  55. 55. 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?
  56. 56. 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 --- ---
  57. 57. 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)