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Thermodynamics

This unit explores the quantitative measurement of energy during phase changes, specifically focusing on the heat of fusion and heat of vaporization. The heat of fusion is the energy needed to melt 1 gram of a solid at its melting point, with water requiring 80.0 cal/g for this process. The heat of vaporization involves the energy necessary to vaporize 1 gram of a liquid, with water needing 539 cal/g. Real-life examples illustrate how to calculate these energies, keeping in mind that during phase changes, temperature remains constant.

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Thermodynamics

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  1. Thermodynamics Unit 10

  2. Quantitative Measure of Energy in Phase Changes Heat of Fusion – amount of energy needed to melt 1 gram of a solid at its melting point Solid + E Liquid For water: 80.0 cal = Latent Heat 1 gram melt (absorb E) freeze (release E) Free Template from www.brainybetty.com

  3. Quantitative Measure of Energy in Phase Changes Heat of Vaporization – amount of energy needed to vaporize 1 gram of a liquid at its boiling point Liquid + Energy Vapor For water: 539 cal = Latent Heat 1 gram vaporize (absorb E) condense (release E) Free Template from www.brainybetty.com

  4. Quantitative Measure of Energy in Phase Changes **These are for phase changes. (Remember, during a phase change, there is no change in T.) For a change in T, use Q = mcDT. Free Template from www.brainybetty.com

  5. Quantitative Measure of Energy in Phase Changes Examples: How many calories are absorbed or released when 20.0 g of ice is melted at 0.00oC? s  l Latent Heat of Fusion = 80.0 cal/g m = 20.0 g Free Template from www.brainybetty.com

  6. Quantitative Measure of Energy in Phase Changes 80.0 cal 20.0 g = 1600 cal 1 g 1.60 x 103 cal absorbed Free Template from www.brainybetty.com

  7. Quantitative Measure of Energy in Phase Changes How many calories are absorbed or released when 15.0 g of water vapor condenses at 100.0oC? g  l Latent Heat of Vaporization = 539 cal/g m = 15.0 g Free Template from www.brainybetty.com

  8. Quantitative Measure of Energy in Phase Changes 539 cal 15.0 g = 8085 cal 1 g 8090 cal released Free Template from www.brainybetty.com

  9. Quantitative Measure of Energy in Phase Changes How many calories are absorbed or released to raise 30.0 g of water from 25.0oC to 75.0oC? No phase change! q = mcDT q = ? m = 30.0 g c = 1.00 cal/goC Ti = 25.0oC Tf = 75.0oC Tf – Ti = 50.0oC Free Template from www.brainybetty.com

  10. Quantitative Measure of Energy in Phase Changes q = mcDT q = (30.0 g)(1.00 cal/goC)(75.0oC – 25.0oC) q = (30.0)(1.00)(50.0) q = 1500 cal q = 1.50 x 103 cal absorbed Free Template from www.brainybetty.com

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