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Understanding Energy Flow During Phase Changes of Matter

This document outlines the essential concepts of energy flow associated with phase changes in matter, particularly water. It explains that energy must be absorbed for phase changes from solid to liquid (melting) and liquid to vapor (vaporization). Conversely, energy is released during vapor to liquid (condensation) and liquid to solid (freezing) transitions. The heat of vaporization and fusion for water is detailed, along with a phase change diagram illustrating the changes. Additionally, the refrigeration cycle's energy interchange process is discussed to show practical applications.

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Understanding Energy Flow During Phase Changes of Matter

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  1. Important Terms & Notes Feb. 27-28, 2014

  2. Energy Flow During Phase Changes of Matter • Energy must be ABSORBED by matter when the phase changes from: • Solid to Liquid and Liquid to Vapor. • Energy must be RELEASED by matter when the phase changes from: • Vapor to Liquid and Liquid to Solid.

  3. Heat of Vaporization • The amount of heat required to change the phase of 1 gram of a substance in liquid form into 1 gram of vapor. Q = mL • For H20: L = 540 cal/g

  4. Heat of Fusion • The amount of heat given up to change the phase of 1 gram of a substance in liquid form into 1 gram of solid form (crystal/ice). Q = mL • For H20: L = 80 cal/g

  5. Phase Change Diagram of H2O

  6. Phase Change Diagram of H2O

  7. Phase Change Diagram of H2O

  8. Phase Change Diagram of H2O

  9. Questions Regarding the Phase Diagram • 1. The phase of water present along "Leg A" of the diagram is: •  ?    vapor •  ?    solid • ?Liquid • 2. The phase change taking place, in the right-to-left direction, along Leg "B" is: •   ?    melting •   ?    boiling •   ?    freezing

  10. Questions Regarding the Phase Diagram • 3. According to the diagram, during a phase change the temperature: •   ?    increases •   ?    remains constant •   ?    Fluctuates • ?    decreases • 4. At normal atmospheric pressure, water boils at: •   ?    100 ºC •   ?    0 ºC •   ?    -20 ºC •   ?    120 ºC

  11. Questions Regarding the Phase Diagram • 5. The phase of water present along "Leg E" of the diagram is: •   ?    solid •   ?    vapor •   ?    liquid • 6. According to the diagram, freezing requires •   ?    absorption of energy •   ?    no energy change •   ?    removal of energy

  12. The Refrigeration Cycle

  13. Energy Interchange in a Refrigerator’s Cooling Cycle • Heat is taken in from the inner compartment as the Refrigerant (liquid) evaporates in the pipes (Evaporator) and changes phase to vapor. • The vapor is compressed and then pumped through a heat exchanger pipe assembly (Condenser) where heat is given up to the outside environment allowing the vapor to condense into liquid.

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