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Ch 12 Gas Laws

Ch 12 Gas Laws. Gases. Ideal Gas---composed of molecules with mass, but with no volume and no mutual attraction between the gas molecules

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Ch 12 Gas Laws

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  1. Ch 12 Gas Laws

  2. Gases • Ideal Gas---composed of molecules with mass, but with no volume and no mutual attraction between the gas molecules • Real Gas---Molecules have mass, volume and an attraction for one another. Real gases behave like ideal gases except at very low temperatures & high pressure.

  3. Gases • Absolute Zero---temperature at which all motion should stop ) -273oC • Absolute Kelvin Scale---based on absolute zero scale 0 K • STP -----OoC or 273 K • 101.3 kPa or 1 atm or 760 mm

  4. Gases • Adiabatic system----allows no heat exchange with the surroundings • Point masses-particles that have no volume or diameter because they are so small and so far apart • Units: • Volume----l, dm3,ml, cc • Pressure-----mm, torr, atm, kPa

  5. Boyle’s Law • Boyle’s Law—states that at constant temperature, the volume of a gas varies inversely with the pressure. • V1/ V2 = P2/P1 • V1P1 = V2P2

  6. Boyle’s Law • Page 424----curve for Boyle’s Law • EX: • The volume of a gas at 25.0 kPa is 300 ml. If the pressure is increased to 99.0 kPa, what will the new volume be. Temperature is constant. • V1P1 = V2P2 • (300ml) (25.0kPa) = V2(99.0 kPa) • V2 = 75.8ml

  7. Boyle’s Law • Page 425----- 1-4 • Show formula and work with answer and correct units • Use factor label method.

  8. Charles’ Law • Charles’ Law—states that at constant pressure the volume of a gas is directly proportional to the Kelvin temperature. • V1/V2 = T1/T2 • V1T2 = V2T1 • Remember: K = 0C + 273

  9. Charles’ Law • Show curve for Charles’ Law on board • Page 427

  10. Charles’ Law • Ex: 20 liters of nitrogen gas at 101.3kPa has a temperature of 250C, what is the volume of this gas at STP? • V1T2 = V2T1 • 20 L X 273K = V2 x 298K • V2 = 18.3 L • ***must show formula and set up with answer and proper units

  11. Charles’ Law • Ex: At STP a gas occupies 200ml, if the volume changes to 300 ml, what is the new temperature at 1atm. • Solve on board

  12. Charles’ Law • Note that if Kelvin temperature doubles then volume doubles!!! • Note too, that if Celsius temp. doubles the volume will increase NOT DOUBLE • If Pressure triples, volume will be 1/3 as large

  13. Gas laws • Given: • Pressure constant, temp. changes from: • 300C to 900C volume increases • 30 K to 90 K volume triples • Temp. constant, pressure changes from: • 1 atm to 2 atm volume decrease by ½ • 4 atm to 2 atm volume doubles

  14. Practice: • Pressure constant, temp. changes from • 200K to 400 K Volume _____ 50 K to 25 K Volume _______ 100 C to 50 C Volume _______ Temp. constant, pressure changes from 4 atm to 2 atm Volume ______ 16 atm to 32 atm Volume ______

  15. Charles’ Law • Page 428 1-4

  16. Combined Gas Law • Sometimes both pressure and temperature will change at the same time. Combined gas law is used when this happens? • V1/ V2 = P2T1/P1T2 • V1P1T2 = V2P2T1 • ****must use Kelvin temp.

  17. Combined law • Ex: 300 ml of gas at STP is heated to 50.00C and the pressure is 460mm.What is the new volume? • Solve on the board.

  18. Gay Lussac’s • Gay-Lussac’s Law---states that if volume is constant, the pressure of a gas is directly proportional to the Kelvin temperature. • P1/P2 = T1/T2 • P1T2 = P2T1 • ****** remember: use Kelvin temperature

  19. Gay Lussac’s • Ex: The pressure of a gas in a tank is 3.2 atm at 22.0 0C. If the temp. rises to 60.00C, what will be the pressure of the gas? • P1T2 = P2T1 • (3.2 atm) ( 333K) = P2(295K) • P2 = 3.61 atm

  20. Gay- Lussac’s Law • page 431 1-4, page 446 # 47,48,49 • Curve for GayLussac’s Law • p 429

  21. Avogradro’s Law Avogradro’s Law V = kn V = volume K = 22.4 L/mol N = number of moles

  22. Avogadro’s Hypothesis • Avogadro’s hypothesis: equal volumes of gases will have the same number of particles at equal pressure and temp. • Mole # of one = Mole # of two • At STP a mole of gas will occupy 22.4 liters and will have 6.02 X 1023 particles

  23. Avogadro’s H. • What volume will 3.5 mols of a gas occupy at STP ? • How many grams of oxygen gas will be contained in a 3.00 l flask at STP?

  24. Avogadro’s • How many grams in 500 cc of nitrogen gas at STP. • 40 grams of neon gas will occupy what volume at STP?

  25. Dalton’s Partial Pressure Law • Dalton’s Partial Pressure Law---states that the total pressure of a system is equal to the sum of all the partial pressures within the system. • Pt = P1 + P2 ……..

  26. Gas Laws • Dalton’s Law—used when a gas is collected over water. • The water vapor is mixed with the gas collected • Water vapor pressure is directly related to temperature

  27. The following gas volumes where collected over water under the conditions indicated. Correct each vol to the vol that the dry gas will occupy at standard pressure. ( Temp is constant) 600 cc at 22oC and 87.3 kPa. ( pressure of water at 22 C is 2.6 kPa.

  28. Gas Laws • Ex: A mixture has O2, CO2, and N2 will have a pressure of .97 atm. What is the partial pressure of O2, if CO2 is .70 atm and N2 is .12 atm?

  29. Gas Laws • What is the pressure of hydrogen collected over water at the temperature of 180 C if the atmospheric pressure is 98.6 kPa.

  30. A mixture of gases with a pressure of 800 mm Hg contains 10% oxygen and 90% nitrogen by volume. What is the partial pressure of the oxygen gas in the mixture?

  31. Graham’s Law • Graham’s Law---states that under identical conditions of temp. and pressure, 2 gases relative diffusion rates vary inversely with the square roots of their molecular masses.

  32. Graham’s Law • Graham’s Law: p 438 # 1

  33. Ideal Gas Law • The Ideal Gas Law combines all other gas laws into one mathematical expression. • V = nRT/P • V = volume ( L or dm3) • Number of mols = n • T= kelvin temp ( must be Kelvins not degrees) • P= pressure ( atm or kPa) • R= universal gas or ideal gas constant

  34. Data Table • 1. Mass of Meter of Mg 1 gram • 2. Mass of Mg used _______g • 3. temp of water ______C • 4. Atmospheric Pressure 99.0 kpa • 5. Volume of H2 collected ______ml • 6. Vapor pressure of water • at temp. collected _______kpa • 7. Volume of Hydrogen collected, • corrected to STP ______ml • 8. Pressure of dry Hydrogen collected ______kPa

  35. Ideal Gas Law • “R” may have the following values: • R = .0821L-atm/mol-K • R = 8.31 dm3 –kPa/ mol-K

  36. Ideal Gas Law • Remember: a mol of gas at STP will occupy 22.4 L( molar volume) • The number of moles of a gas is directly proportional to its volume at STP

  37. Ideal Gas Law • What is the volume of 22 grams of carbon dioxide at 10 C and 98.0 kpa pressure?

  38. What is the temperature of 80 grams of nitrogen gas filling a 40 ml container at a pressure of 4 atmospheres? • How many grams of methane will occupy 12 ml at STP?

  39. Ideal Gas Law • What is the pressure of 3 moles of ammonia at 450C which occupy 5 liters. • Solve on board

  40. Ideal Gas Law • page 435 1-4, • Page 442 # 7,8,9 • Page 447 52-56

  41. Ideal Gas Law • The ideal gas law can be used to determine the density and the molecular mass of a gas. • M = molecular mass • “n” = m (mass) /M ( molecular mass) • “n” = m/M • V = mRT/MP

  42. Ideal Gas Law • D = m/v • so • M =DRT/P.

  43. Ideal Gas Law • What is the molar mass of a pure gas that has a density of 1.4g/L at STP ? • M = DRT/P • M = ( 1.4g/l)(.0821L-atm/mol K)(273K)/1atm • M = 31.4 g/mol

  44. Ideal Gas Law • 1.What is the molecular mass of a gas if 150.0 cm3 have a mass of 0.922 g at 99C and 107.0 kPa ? • 2. What is the molecular mass of a gas if 3.59 g of it occupy 4.34 dm3 at 99.2 kPa and 310C? • 3. What is the molecular mass of a gas if 0.858 g of it occupies 150.0 cm3 at 106.3 kPa and 20C ? • Page 483 old text

  45. Practice Problems • Page 448-449 • 72-85,90-92, 95 a, 99,107

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