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B. Changing Phases

Temperature as we heat a pure substance. B. Changing Phases. During a phase change, all the energy added does not cause a change in temperature. Boiling water stays at 100 o C, it does not heat up Freezing water stays at 0 o C, it does not cool down. All energy added goes to change the phase.

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B. Changing Phases

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  1. Temperature as we heat a pure substance B. Changing Phases During a phase change, all the energy added does not cause a change in temperature Boiling water stays at 100oC, it does not heat up Freezing water stays at 0oC, it does not cool down All energy added goes to change the phase Latent energy Potential energy stored as a change of phase Heating curve demonstration

  2. KE PE KE PE Temp KE PE KE PE KE PE Time 1. Heating Curve Gas phase Boiling Melting No temp change Solid phase No temp change Liquid phase Phases KE (temp) increases, PE does not change Phase change KE does not change, PE changes

  3. Temp Heating curve Time 2. Cooling Curve Reverse of Heating Curve Condensation Freezing or Crystallization Reverse of Boiling Condensation Occurs at the same temp as boiling Reverse of Melting Freezing or Crystallization Occurs at the same temp as melting

  4. C. Energy needed to change phases 1. Heat of Fusion Temperature does not change during a phase change Energy added is used to change the phase Heat of Fusion Hf Energy needed to turn 1 g of a solid into 1 g of a liquid Hf of water 334 joules/g Found on the first page of your reference tables! Example - How much energy is required to melt 10.0 g of ice at 0oC to 10.0 g of water at 0oC? Q = Hf x m Q = 334 x 10.0 g Q = 3340 joules 3340 joules

  5. How much ice at 0oC can we melt to water at 0oC using 1.36 Kjoules of heat? Q = Hf x m 1360 joules = 334 x m 4.0718 g 4.07 g

  6. 4. Heat of vaporization Hv Energy needed to boil 1 g of a liquid into 1 g of a gas For water, Hv = 2259 J/g To boil, add 2259 J To condense, remove 2259 J Heat of Vaporization = Heat of Condensation 1. How much energy is needed to completely boil 50.0 g of water at 100oC to 50.0 g of steam at 100oC? Q =m x Hv Q = 2259 x 50.0 Q = 112,950 J 113,000 J 2. How much water at 100oC can we boil to steam at 100oC using 11.63 kJ of heat? Q = m x Hv 11,630 = 2259 x m 5.148295706 g = m 5.148 g

  7. E. Solids 1. Characteristics Atoms and molecules are locked in one place They do not change positions Pure substances create their own particular geometric shape Crystal - Repeating geometric structure Shape depends on the type of atoms in a solid Pattern is called a Crystal lattice

  8. 3. Sublimation Going from solid directly to the gas phase Skips the liquid phase 2 important examples CO2(s) CO2(g) I2(s) I2(g)

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