Phase changes

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Phase changes

  1. 1. Phase Changes
  2. 2. Phase Change It is a transition between solid, liquid, and gaseous phases typically involve large amounts of energy compared to the specific heat.
  3. 3. Latent Heat Is the HEAT released or absorbed by a body during a change of state without change of temperature. Heat of FusionEnergy is absorbed from the air to melt solid ice intoliquid water without any change is temperature. Heat of VaporizationEnergy is also absorbed to change water into steamwithout any change in temperature.
  4. 4. Phase Change Diagram condensation evaporation Freezing Melting
  5. 5. Simple RecallThe change from solid to liquid is. MeltingThe change from liquid to solid. Freezing
  6. 6. Simple RecallThe change from gas to liquid CondensationThe change from liquid to gas Vaporization
  7. 7. Simple RecallThe change from solid to gas. SublimationThe change from gas to solid. Deposition
  8. 8. Heat of Phase Change Calorimetry Nature demands that energy always be conserved: The heat lost by objects of decreasing temperature must be equal to the heat gained by objects of increasing temperature. ..Or the state of measurement of exchanging quantities of heat
  9. 9. Here, if heat is added to a body, then the value ispositive; and if the heat is taken from a body, then the value is negative. Since energy (in this case heat) is always conserved, then:  Heat added (+) + Heat taken (-) = 0  Heat added = heat taken
  10. 10. Problem Solving A glass weighing 30g contains 85g of water at 25o C. How much ice at 0 O C will be needed to bring the temperature down to 5 O C? The specific heat of glass is 0.16cal/g, and that of water is 1.00 cal/g. O O Given : m glass= 30g , m water = 85g at 25 C ,T mix =5 C Find : m ice
  11. 11. Problem Solving Solution: Let H (heat absorbed by ice) --- 1 (m )(80cal/g) ice H 2 (heat absorbed by melted ice) --- (m ice )(1.00cal/g .OC )(25 OC – 5O C) H 3 (heat given off by glass) --- (30 g)(0.16cal/g . C )(25O C – 5O C) H 4 (heat given off by water) ---

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