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Heat of Fusion

Heat of Fusion. Hfus = 80 cal/g = 334 J/g. Latent Heat. Take 1 kg of water from –10 o C up to 150 o C we can plot temperature rise against absorbed heat. steam (water vapor). 100 C. ice. water. 0 C. -10 C. H f = 80 cal/g. H v = 540 cal/g. Q heat absorbed.

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Heat of Fusion

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  1. Heat of Fusion

  2. Hfus = 80 cal/g = 334 J/g

  3. Latent Heat • Take 1 kg of water from –10 oC up to 150 oC we can plot temperature rise against absorbed heat steam (water vapor) 100 C ice water 0 C -10 C Hf = 80 cal/g Hv = 540 cal/g Q heat absorbed Hf is the heat of fusion Hv is the heat of vaporization

  4. LAW OF CONSERVATION OF ENERGY Energy cannot be created or destroyed.

  5. Law of Conservation of Energy The amount of energy you must give up from one system, to get a particular thing to happen to another system, is always the same. Energy lost in one place Energy gained somewhere else =

  6. Exothermic and Endothermic Processes • Exothermic • process that releases energy to the surroundings • Endothermic (melting) • process that absorbs energy from the surroundings • (need heat to make the reaction happen) • Examples

  7. Heat vs Temperature Heat energy is the collective random motion of molecules, and temperature is a measure of how fast the molecules are moving.

  8. Heating Curve for Water E. Steam abosrbs heat & increases temp. D. Water boils & absorbs latent heat of vaporization vaporization E gas D 100 condensation C C. Rise in Temp liquid water absorbs heat liquid melting Temperature (oC) B 0 B. Absorption of Latent (hidden) Heat A freezing solid A. Rise in Temp as ice absorbs Heat added LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 487

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