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Understanding Phase Changes in Chemistry: Heat Energy and State Transitions

Phase changes are critical processes in chemistry where substances transition between solid, liquid, and gas phases. These changes involve the absorption or release of heat energy, affecting the material's state. Key phase changes include melting (solid to liquid), vaporization (liquid to gas), condensation (gas to liquid), freezing (liquid to solid), and sublimation (solid to gas). Each phase change impacts heat energy differently—melting and vaporization absorb heat, while freezing and condensation release it. Understanding these concepts is essential for studies in thermodynamics and physical chemistry.

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Understanding Phase Changes in Chemistry: Heat Energy and State Transitions

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  1. Topic: Chemistry Aim: Explain the different types of phase changes and the energy changes involved. Do Now: ON NOTES SHEET HW: Ditto – Periodic Tables Families Review (last page of Periodic Table Notes Packet)

  2. http://www.youtube.com/watch?v=XaDxwe8l3us&feature=related

  3. Phase Changes • Involves the absorption OR release of heat (energy).

  4. Substance absorbs heat energy

  5. Melting • Solid  liquid • Solid ABSORBS heat energy Substance absorbs heat energy

  6. Melting points of different substances • Iron: 1536ºC • Gold: 1063ºC • Glucose: 150ºC • Urea: 132-134ºC

  7. Vaporization • Liquid  gas • Liquid ABSORBS heat energy • When it occurs on surface of liquid: evaporation GAS Liquid absorbs heat energy LIQUID

  8. Boiling points of different substances • Alcohol (Ethanol): 79ºC • Iodine: 184.3ºC • Mercury: 356.9ºC • Olive oil: 300ºC • Jet fuel: 163ºC

  9. Condensation • Gas  liquid • Gas LOSES heat energy GAS Gas loses heat energy LIQUID

  10. Freezing • Liquid  solid • Liquid LOSES heat energy Substance loses heat energy

  11. Sublimation • Solid  Gas • No liquid phase • Ex: dry ice GAS Solid absorbs heat energy Solid

  12. Moth balls commonly undergo the process of sublimation. Sublimation is the process in which a solid changes directly to its gaseous phase, skipping the liquid phase.

  13. And an animation of the phase changes of water

  14. Let’s summarize… • List the different types of phase changes. 2. Explain what happens to heat energy in each phase change.

  15. 1. When a liquid becomes a solid, energy • does not change • is released • is absorbed • is first absorbed, then released

  16. 2. _______ is the process in which liquid changes to gas below the boiling point.   Sublimation Condensation Evaporation Combustion

  17. 3. On a hot day, the outside of a glass containing a cold drink becomes frosty. When touching the glass, it feels • water that has passed through the glass • water that has condensed from a gas in the air • water that has solidified • water that has absorbed energy

  18. 4. The change of a liquid to a solid is called freezing Melting sublimation vaporization

  19. 5. During which of the following processes is there a decrease in the heat content of the form of water indicated? • Ice as it forms on a lake • Water droplets as they fall to the ground • Water as it evaporates from a pond • Snow as it melts on a mountainside

  20. 6. When substances go directly from the solid phase to the gas phase, the phase change is called sublimation condensation evaporation vaporization

  21. E D condensing 100 boiling C Temperature º C. B freezing 0 melting A Heat (thermal energy)

  22. http://www.youtube.com/watch?v=vDZhUkp30tE&feature=related

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