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Important Terms & Notes

This document outlines the essential principles governing the energy flow during phase changes of matter, focusing on water (H2O). It explains how energy must be absorbed for transitions from solid to liquid and liquid to vapor, while energy is released during the changes from vapor to liquid and liquid to solid. Key concepts like heat of vaporization and heat of fusion for water are highlighted, alongside a phase change diagram. Important questions are posed to evaluate understanding of the phase relationships and energy changes in a refrigeration cycle.

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Important Terms & Notes

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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. Heat Diagram of H2O

  6. Heat Diagram of H2O

  7. Heat 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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