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Heat Changes

Heat Changes. Enthalpy. E N T H A L P Y - H. heat content in matter:. E N T H A L P Y - H. heat content in matter: natural systems tend to go from a state of high energy to a state of low energy. E N T H A L P Y. The phases of matter represent "classes" of molecular motion found

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Heat Changes

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  1. Heat Changes

  2. Enthalpy

  3. E N T H A L P Y - H heat content in matter:

  4. E N T H A L P Y - H heat content in matter: natural systems tend to go from a state of high energy to a state of low energy.

  5. E N T H A L P Y The phases of matter represent "classes" of molecular motion found at different temperatures. Solid Gas Liquid

  6. E N T H A L P Y Kinetic Energy X The phases of matter represent "classes" of molecular motion found at different temperatures.

  7. E N T H A L P Y HEAT X The phases of matter represent "classes" of molecular motion found at different temperatures.

  8. E N T H A L P Y q = U + P V q = heat gained or lost U = internal energy P = Pressure V = volume

  9. E N T H A L P Y Hfus - heat of fusion As energy is added to a solid at its melting point, ALL the energy is used to increase the kinetic energy of the molecules during the phase change.

  10. E N T H A L P Y Hfus - heat of fusion The amount of heat needed to change one gram of a solid into a liquid at its melting point.

  11. Temperature Rise Heat Added

  12. Every phase change is accompanied by a change in the energy of the system.

  13. As the temperature of a solid increases, its particle vibration increases.

  14. When a solid melts, its particles are freed to move with respect to one another.

  15. This melting process is called fusion.

  16. The increased freedom of motion of the molecules or ions comes at a price...

  17. measured by the heat of fusion, or enthalpy of fusion, DHfus

  18. As the temperature of a liquid increases, the molecules move with increasing energy.

  19. When increasing temperature, the concentration of gas-phase molecules just above the surface of the liquid increases.

  20. These gas-phase molecules exert a pressure on the liquid called vapor pressure.

  21. This vapor pressure increases with temperature until it equals the atmospheric pressure.

  22. This is the boiling point of the liquid.

  23. The energy required to cause this transition..

  24. is called the heat of vaporization or enthalpy of vaporization, DHvap

  25. solid/liquid phase change q = m Hfus q = heat gained or lost m = mass DHfus = heat of fusion

  26. E N T H A L P Y Hfus H2O = 334 J/g Hfus lead = 24.72 J/g

  27. E N T H A L P Y As energy is added to a liquid at its boiling point, ALL the energy is used to increase the kinetic energy of the molecules during the phase change.

  28. E N T H A L P Y Hvap- heat of vaporization The amount of heat needed to change one gram of a liquid into a gas at its boiling point.

  29. liquid/gas phase change q = m Hvap q = heat gained or lost m = mass DHvap = heat of vaporization

  30. E N T H A L P Y HvapH2O = 2260 J/g

  31. change temp within phase q = m TCp q = heat gained or lost m = mass DT = “change in temperature” Cp = specific heat capacity

  32. Specific Heat Capacity The heat required to raise the temperature of one gram of a substance by one Celsius degree.

  33. Specific Heat Capacity Cp of ice = 2.06 J/g.Co Cp of water = 4.18 J/g.Co Cp of steam = 2.02 J/g.Co Cp of copper = .385 J/g.Co

  34. q=mTCp - change temp q=mHvap - change phase q=mTCp - change temp q=mHFUS- change phase q=mTCp - change temp

  35. Sixteenth Lab Heat of Fusion of Ice

  36. Change temp of ice Melt ice Change temp of liquid water Vaporize water Change temp of vapor Add total heat used How much heat is needed to convert 250 grams of ice at -30 oC to vapor at 150 oC?

  37. Step 1 raise temp of ice q = m DT Cp q = (250g) (30 Co) (2.06 J/g. Co) q = 15,450 Joules

  38. Step 2 melt ice q = m DHfus q = (250g) (334 J/g) q = 83,500 Joules

  39. Step 3 raise temp of liquid water q = m DT Cp q = (250g) (100 Co) (4.18 J/g. Co) q = 104,500 Joules

  40. Step 4 vaporize liquid water q = m DHvap q = (250g) (2260 J/g) q = 565,000 Joules

  41. Step 5 raise temp of water vapor q = m DT Cp q = (250g) (50 Co) (2.02 J/g. Co) q = 25,250 Joules

  42. Step 6 q = 15,450 83,500 104,500 565,000 25,250 q = 794,000 Joules

  43. What is Specific Heat Capacity

  44. Which has the greater? Specific Heat Capacity H2O Fe or

  45. Specific Heat Capacity - 13 min

  46. A Calorimeter is used to measure heat change

  47. Calorimetry - 13 min

  48. Seventeenth Lab Specific Heat of a Metal

  49. Eighteenth Lab Lab Burners and BTUs

  50. Enthalpy end

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