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Kinetic Molecular Theory (KMT)

Kinetic Molecular Theory (KMT). AKA: Kinetic Theory of Molecules (KTM). Energy is the capacity to do work. Energy is measured in Joules 1 Joule of energy can raise 1 N of weight exactly 1 meter 1 J=1Nm. Energy is the capacity to do work. Forms include: Kinetic energy

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Kinetic Molecular Theory (KMT)

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  1. Kinetic Molecular Theory (KMT) AKA: Kinetic Theory of Molecules (KTM)

  2. Energy is the capacity to do work. Energy is measured in Joules 1 Joule of energy can raise 1 N of weight exactly 1 meter 1 J=1Nm

  3. Energy is the capacity to do work. Forms include: • Kinetic energy • Gravitational potential energy • Elastic potential energy • Electrical energy • Chemical potential energy • Heat

  4. Energy is the capacity to do work. Forms include: • Kinetic energy • Gravitational potential energy • Elastic potential energy • Electrical energy • Chemical potential energy • Heat …of the greatest interest to a chemist

  5. Exothermic process System Surroundings Energy An exothermic process releases energy

  6. Endothermic process System Surroundings Energy An endothermic process absorbs energy

  7. If you add heat to a sample, it may… a) b) c) d)

  8. If you add heat to a sample, it may… a) warm up. b) melt c) boil d) expand (tough to calculate, don’t bother)

  9. Let’s try to warm up a cup of cold coffee. Step 1: Add heat.

  10. Let’s try to warm up a cup of cold coffee. Step 1: Add heat. Well, that was easy.

  11. Let’s try to warm up a cup of cold coffee. How could you add half as much heat?

  12. Let’s try to warm up a cup of cold coffee. How could you add half as much heat? a) b) c)

  13. Let’s try to warm up a cup of cold coffee. How could you add half as much heat? a) Raise the temperature only half as much. b) c)

  14. Let’s try to warm up a cup of cold coffee. How could you add half as much heat? a) Raise the temperature only half as much. b) Use half as much coffee (and cup) c)

  15. Let’s try to warm up a cup of cold coffee. How could you add half as much heat? a) Raise the temperature only half as much. b) Use half as much coffee (and cup) c) Use a different substance

  16. The effect of heat (q) • q depends on: • The mass of the sample (m) • The change in temperature (DT) • The nature of the sample (C)

  17. The effect of heat (q) • q depends on: • The mass of the sample (m) • The change in temperature (DT) • The nature of the sample (C) C is the specific heat capacity for a given substance. Its units are (J/goC)

  18. If you add heat to a sample, it may… a) warm up. q=mCDT b) melt c) boil d) expand (tough to calculate, don’t bother)

  19. q=mCDT • q – heat, in Joules • m –mass, in grams • C –specific heat capacity, in J/goC • DT—change in temperature (Tfinal-Tinitial)

  20. Cwater=4.184 J/goC • Cwater =4.2 J/goC • Cethanol =2.4 J/goC • Cice =2.1 J/goC • CAl =.90 J/goC • CFe =.46 J/goC • Cglass =.50 J/goC • CAg =.24 J/goC

  21. How much heat? • How much heat does it take to raise 50.g water from 15oC to 80.oC? • q=mCDT

  22. How much heat? • How much heat does it take to raise 50.g water from 15oC to 80.oC? • q=mCDT = 50.g x 4.18 J/goC x (80.oC-15oC)

  23. How much heat? • How much heat does it take to raise 50.g water from 15oC to 80.oC? • q=mCDT = 50.g x 4.18 J/goC x (80.oC-15oC) = 50.g x 4.18 J/goC x (65oC)

  24. How much heat? • How much heat does it take to raise 50.g water from 15oC to 80.oC? • q=mCDT = 50.g x 4.18 J/goC x (80.oC-15oC) = 50.g x 4.18 J/goC x (65oC) =14000 J (14 kJ)

  25. What is the change in temperature? • If you add 1550 J to 12 g water, how much will it heat up? • DT =q/mC

  26. What is the change in temperature? • If you add 1550 J to 12 g water, how much will it heat up? • DT =q/mC= 1550 J / (12 g x 4.18 J/goC )

  27. What is the change in temperature? • If you add 1550 J to 12 g water, how much will it heat up? • DT =q/mC= 1550 J / (12 g x 4.18 J/goC ) = 31oC

  28. What is the change in temperature? • If you add 1550 J to 12 g water, how much will it heat up? • DT =q/mC= 1550 J / (12 g x 4.18 J/goC ) = 31oC If the temperature starts at 25oC, it will heat up to …

  29. What is the change in temperature? • If you add 1550 J to 12 g water, how much will it heat up? • DT =q/mC= 1550 J / (12 g x 4.18 J/goC ) = 31oC If the temperature starts at 25oC, it will heat up to 56oC

  30. Calorimetry • --the measurement of heat.

  31. Calorimetry • --the measurement of heat. • If one thing gains heat…

  32. Calorimetry • --the measurement of heat. • If one thing gains heat… …something else lost it.

  33. If 75 g of a metal at 96oC is placed in 58 g of water at 21oC and the final temperature reaches 35oC, what is the specific heat capacity of the metal?

  34. Step 1 • How much heat did the water gain?

  35. Step 1 • How much heat did the water gain? q=mCDT Mass of water, in grams Specific heat of water, 4.18 J/goC Change in the temperature of water, in oC

  36. Step 2 • How much heat did the metal lose?

  37. Step 2 • How much heat did the metal lose? • Heat lost = - heat gained • qlost=-qgained

  38. Step 3 • What is the specific heat capacity of the metal?

  39. Step 3 • What is the specific heat capacity of the metal? C=q/mDT Heat lost by metal Mass of metal, in grams Change in the temperature of metal, in oC Specific heat of metal, in J/goC

  40. If 75 g of a metal at 96oC is placed in 58 g of water at 21oC and the final temperature reaches 35oC, what is the specific heat capacity of the metal? .74 J/goC

  41. Thermochemistry • 2H2(g)+O2(g) 2H2O(g)+ 443,000 J • Two moles of hydrogen gas reacts with one mole of oxygen gas to form two moles of water vapor, releasing 443 kJ of heat.

  42. Chemical Energy • Chemical energy (enthalpy) is stored in bonds.

  43. Chemical Energy • Chemical energy (enthalpy) is stored in bonds. • Forming bonds releases energy • Breaking bonds requires energy

  44. Chemical Energy • Chemical energy (enthalpy) is stored in bonds. • Forming bonds is exothermic • Breaking bonds is endothermic

  45. Chemical Energy • Chemical energy (enthalpy) is stored in bonds. • Exothermic reactions have a negative change in enthalpy • Endothermic reactions have a positive change in enthalpy

  46. Thermochemistry 2H2 +O22H2O Breaking these bonds requires energy

  47. Thermochemistry 2H2 +O22H2O Breaking these bonds requires energy

  48. Thermochemistry 2H2 +O22H2O Breaking these bonds requires energy Forming these bonds releases a lot more energy

  49. The mass to heat problem g 1 mol kJ kJ g mol The heat of reaction, DHrxn

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