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17.3 Heat in Changes of State > Heats of Vaporization and Condensation Enthalpy changes accompany changes in state. Slide 1 of 35 © Copyright Pearson Prentice Hall 17.3 Heat in Changes of State > Heats of Fusion and Solidification The molar heat of fusion (∆Hfus) is the heat absorbed by one mole of a solid substance as it melts to a liquid at a constant temperature. The molar heat of solidification (∆Hsolid) is the heat lost when one mole of a liquid solidifies at a constant temperature. Slide 2 of 35 © Copyright Pearson Prentice Hall 17.3 Heat in Changes of State > Heats of Fusion and Solidification The quantity of heat absorbed by a melting solid is exactly the same as the quantity of heat released when the liquid solidifies; that is, ∆Hfus = –∆Hsolid. Slide 3 of 35 © Copyright Pearson Prentice Hall SAMPLE PROBLEM 17.4 Slide 4 of 35 © Copyright Pearson Prentice Hall SAMPLE PROBLEM 17.4 Slide 5 of 35 © Copyright Pearson Prentice Hall SAMPLE PROBLEM 17.4 Slide 6 of 35 © Copyright Pearson Prentice Hall SAMPLE PROBLEM 17.4 Slide 7 of 35 © Copyright Pearson Prentice Hall Practice Problems for Sample Problem 17.4 Problem Solving 17.21 Solve Problem 21 with the help of an interactive guide tutorial. Slide 8 of 35 © Copyright Pearson Prentice Hall 17.3 Heat in Changes of State > Heats of Vaporization and Condensation Heats of Vaporization and Condensation How does the quantity of heat absorbed by a vaporizing liquid compare to the quantity of heat released when the vapor condenses? Slide 9 of 35 © Copyright Pearson Prentice Hall 17.3 Heat in Changes of State > Heats of Vaporization and Condensation The amount of heat necessary to vaporize one mole of a given liquid is called its molar heat of vaporization (∆Hvap). The amount of heat released when 1 mol of vapor condenses at the normal boiling point is called its molar heat of condensation (∆Hcond). Slide 10 of 35 © Copyright Pearson Prentice Hall 17.3 Heat in Changes of State > Heats of Vaporization and Condensation The quantity of heat absorbed by a vaporizing liquid is exactly the same as the quantity of heat released when the vapor condenses; that is, ∆Hvap = –∆Hcond. Slide 11 of 35 © Copyright Pearson Prentice Hall 17.3 Heat in Changes of State > Heats of Vaporization and Condensation Slide 12 of 35 © Copyright Pearson Prentice Hall 17.3 Heat in Changes of State > Heats of Vaporization and Condensation Slide 13 of 35 © Copyright Pearson Prentice Hall SAMPLE PROBLEM 17.5 Slide 14 of 35 © Copyright Pearson Prentice Hall SAMPLE PROBLEM 17.5 Slide 15 of 35 © Copyright Pearson Prentice Hall SAMPLE PROBLEM 17.5 Slide 16 of 35 © Copyright Pearson Prentice Hall SAMPLE PROBLEM 17.5 Slide 17 of 35 © Copyright Pearson Prentice Hall Practice Problems for Sample Problem 17.5 Problem-Solving 17.24 Solve Problem 24 with the help of an interactive guided tutorial. Slide 18 of 35 © Copyright Pearson Prentice Hall 17.3 Heat in Changes of State > Heat of Solution Heat of Solution What thermochemical changes can occur when a solution forms? Slide 19 of 35 © Copyright Pearson Prentice Hall 17.3 Heat in Changes of State > Heat of Solution During the formation of a solution, heat is either released or absorbed. The enthalpy change caused by dissolution of one mole of substance is the molar heat of solution (∆Hsoln). Slide 20 of 35 © Copyright Pearson Prentice Hall 17.3 Heat in Changes of State > Heat of Solution When ammonium nitrate crystals and water mix inside the cold pack, heat is absorbed as the crystals dissolve. Slide 21 of 35 © Copyright Pearson Prentice Hall SAMPLE PROBLEM 17.6 Slide 22 of 35 © Copyright Pearson Prentice Hall SAMPLE PROBLEM 17.6 Slide 23 of 35 © Copyright Pearson Prentice Hall SAMPLE PROBLEM 17.6 Slide 24 of 35 © Copyright Pearson Prentice Hall SAMPLE PROBLEM 17.6 Slide 25 of 35 © Copyright Pearson Prentice Hall Practice Problems for Sample Problem 17.6 Problem-Solving 17.26 Solve Problem 26 with the help of an interactive guided tutorial. Slide 26 of 35 © Copyright Pearson Prentice Hall 17.3 Section Quiz. Assess students’ understanding of the concepts in Section 17.3. Continue to: -or- Launch: Section Quiz Slide 27 of 35 © Copyright Pearson Prentice Hall 17.3 Section Quiz. 1. The molar heat of condensation of a substance is the same, in magnitude, as its molar heat of a. formation. b. fusion. c. solidification. d. vaporization. Slide 28 of 35 © Copyright Pearson Prentice Hall 17.3 Section Quiz 2. The heat of condensation of ethanol (C2H5OH) is 43.5 kJ/mol. As C2H5OH condenses, the temperature of the surroundings a. stays the same. b. may increase or decrease. c. increases. d. decreases. Slide 29 of 35 © Copyright Pearson Prentice Hall 17.3 Section Quiz 3. Calculate the amount of heat absorbed to liquefy 15.0 g of methanol (CH3OH) at its melting point. The molar heat of fusion for methanol is 3.16 kJ/mol. a. 1.48 kJ b. 47.4 kJ c. 1.52 103 kJ d. 4.75 kJ Slide 30 of 35 © Copyright Pearson Prentice Hall 17.3 Section Quiz 4. How much heat (in kJ) is released when 50 g of NH4NO3(s), 0.510 moles, are dissolved in water? ssoln = 25.7 kJ/mol a. 12.85 kJ b. 13.1 kJ c. 25.7 kJ d. 1285 kJ Slide 31 of 35 © Copyright Pearson Prentice Hall END OF SHOW