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Chapter 10 Gases

Chemistry, The Central Science , 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten. Chapter 10 Gases. John Bookstaver St. Charles Community College St. Peters, MO  2006, Prentice Hall, Inc. Bell work. Turn your chapter 10 outline into the tray .

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Chapter 10 Gases

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  1. Chemistry, The Central Science, 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten Chapter 10Gases John Bookstaver St. Charles Community College St. Peters, MO  2006, Prentice Hall, Inc.

  2. Bell work • Turn your chapter 10 outline into the tray. • List the properties of gases. How do they differ from solids and liquids? • What are some of the main formulas in this chapter?

  3. Agenda • Bell work • Discuss review project • Overview of chapter 10 • 10.1-10.6 • HW: Continue reviewing for test! Chapters 6-9, 10?; Thursday, Dec 1

  4. Review project • I’m in the midst of creating a rubric/guideline for a project. It’ll be student-led review during review week. You’ll work with a partner to create an outline of your chapter, sample problems, and a presentation of the material. Tomorrow you’ll get a description, rubric, and have time in class to work on it.

  5. Breakdown • You will be responsible for one of the following topic groupings: • Chapters 1-3 • Chapter 4 • Chapter 5 • Chapters 6 & 7 • Chapter 8 & 9

  6. Chapter 10 – Main points

  7. Pressure and volume • What is the relationship between pressure and volume? • Inversely proportional • Meaning? • When one goes up, the other goes down

  8. Temperature and volume • What is the relationship between temperature and volume? • Directly proportional • Meaning? • When one goes up, the other goes up

  9. Quantity and volume • What is the relationship between quantity and volume? • Directly proportional • Meaning? • When one goes up, the other goes up

  10. Equations • PV=nRT • P1 V1 = P2 V2 • P1 V1 / T1 = P2 V2 / T2 • Ptotal = Pgas 1 + Pgas 2 + Pgas 3 + …. • Need mole fraction moles of gas 1/total moles of gas • Remember that you can get mass from n (# of moles) and you can find density as well

  11. Start with PV=nRT We know that n= mass/Molar mass Density is mass/V  That’s what we want on one side of the equation

  12. Kinetic Molecular Theory Describes ideal gases 5 postulates Molecules in continuous, random motion Negligible volume No attractive forces between molecules Collisions are elastic Average kinetic energy is proportional to absolute temperature

  13. Do larger molecules move faster or more slowly than smaller molecules? Larger move more slowly Affects effusion rate and root mean square (speed of molecule with average KE)

  14. Under what conditions do gases tend to deviate from ideal behavior the most? High pressure Low temperature In general, why do gases deviate from ideal behavior? Gas molecules have finite volumes and molecules are attracted to one another

  15. Characteristics of Gases • Unlike liquids and solids, they • Expand to fill their containers. • Are highly compressible. • Have extremely low densities.

  16. Gases are generally of very low molecular mass. • Gases have high kinetic energies. • In gases, the distance between molecules is relatively large. • In gases, the attractions between molecules are large.

  17. Gases are generally of very low molecular mass. • Gases have high kinetic energies. • In gases, the distance between molecules is relatively large. • In gases, the attractions between molecules are large.

  18. F A P = Pressure • Pressure is the amount of force applied to an area. • Atmospheric pressure is the weight of air per unit of area.

  19. Units of Pressure • You should know: 760 torr = 760 mmHg 1atm = 760 torr 760 torr = 101.325 kPa

  20. Units of Pressure • Pascals • 1 Pa = 1 N/m2 • Bar • 1 bar = 105 Pa = 100 kPa

  21. Units of Pressure • mm Hg or torr • These units are literally the difference in the heights measured in mm (h) of two connected columns of mercury. • Atmosphere • 1.00 atm = 760 torr

  22. The height of the column increases because atmospheric pressure decreases with increasing altitude. • The height of the column decreases because atmospheric pressure decreases with increasing altitude. • The height of the column decreases because atmospheric pressure increases with increasing altitude. • The height of the column increases because atmospheric pressure increases with increasing altitude.

  23. The height of the column increases because atmospheric pressure decreases with increasing altitude. • The height of the column decreases because atmospheric pressure decreases with increasing altitude. • The height of the column decreases because atmospheric pressure increases with increasing altitude. • The height of the column increases because atmospheric pressure increases with increasing altitude.

  24. Manometer Used to measure the difference in pressure between atmospheric pressure and that of a gas in a vessel.

  25. Sample exercises 10.1 and 10.2

  26. Standard Pressure • Normal atmospheric pressure at sea level. • It is equal to • 1.00 atm • 760 torr (760 mm Hg) • 101.325 kPa

  27. Boyle’s Law The volume of a fixed quantity of gas at constant temperature is inversely proportional to the pressure.

  28. Boyle’s Law

  29. PV = k • Since • V = k (1/P) • This means a plot of V versus 1/P will be a straight line. As P and V areinversely proportional A plot of V versus P results in a curve.

  30. The volume change cannot be predicted without knowing the type of gas. • The volume change cannot be predicted without knowing the amount of gas. • As you double the pressure, the volume decreases to half its original value. • As you double the pressure, the volume increases to twice its original value.

  31. The volume change cannot be predicted without knowing the type of gas. • The volume change cannot be predicted without knowing the amount of gas. • As you double the pressure, the volume decreases to half its original value. • As you double the pressure, the volume increases to twice its original value.

  32. V T = k • i.e., Charles’s Law • The volume of a fixed amount of gas at constant pressure is directly proportional to its absolute temperature. A plot of V versus T will be a straight line.

  33. Yes, because volume is proportional to temperature. • No. The volume decreases but it doesn’t decrease to half because the volume is proportional to temperature on the Kelvin scale (not the Celsius scale).

  34. Yes, because volume is proportional to temperature. • No. The volume decreases but it doesn’t decrease to half because the volume is proportional to temperature on the Kelvin scale (not the Celsius scale).

  35. V = kn • Mathematically, this means Avogadro’s Law • The volume of a gas at constant temperature and pressure is directly proportional to the number of moles of the gas.

  36. Sample exercise 10.3

  37. Combining these, we get nT P V Ideal-Gas Equation • So far we’ve seen that V 1/P (Boyle’s law) VT (Charles’s law) Vn (Avogadro’s law)

  38. Ideal-Gas Equation The constant of proportionality is known as R, the gas constant.

  39. nT P nT P V V= R Ideal-Gas Equation The relationship then becomes or PV = nRT

  40. At STP there is one mole or 6.022  1023 molecules (Avogadro’s number). • At STP there is 1 mol of molecules. • At STP there are 22.4 mol of molecules. • More information is needed, because the number of molecules depends on the type of gas.

  41. At STP there is one mole or 6.022  1023 molecules (Avogadro’s number). • At STP there is 1 mol of molecules. • At STP there are 22.4 mol of molecules. • More information is needed, because the number of molecules depends on the type of gas.

  42. Sample exercise 10.4-10.6

  43. Bell work • Aluminum reacts with iodine. I have 5 moles of aluminum. How much iodine do I need to react completely with the aluminum? How much product can I expect?

  44. Agenda • Bell work • Overview of project • Time to work on project • HW: Finish sample problems in chapter 10, continue studying for Thursday’s test (chapters 6-10) • If you want your overviews, come see me after school and I’ll give them to you

  45. Bell work • A large natural-gas storage tank is arranged so that the pressure is maintained at 2.20 atm. On a cold day in December when the temperature is -15⁰C (4⁰F), the volume of the gas is 28,500 ft3. What is the volume of the same quantity of gas on a warm July day when the temperature is 31⁰C (88 ⁰F)?

  46. Agenda • Bell work • Finish chapter 10 • Time to work on HW problems and sample exercises • HW: Test on Thursday! Covers chapters 6-10! Don’t forget about your review projects!

  47. n V P RT = Densities of Gases If we divide both sides of the ideal-gas equation by V and by RT, we get

  48. m V P RT = Densities of Gases • We know that • moles  molecular mass = mass n  = m • So multiplying both sides by the molecular mass ( ) gives

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