Slide 1 of 35 © Copyright Pearson Prentice Hall > Heat in Changes of State Heats of Vaporization and Condensation Enthalpy changes accompany changes in state. 17.3

Slide 2 of 35 © Copyright Pearson Prentice Hall > Heat in Changes of State Heats of Fusion and Solidification The molar heat of fusion (∆H fus ) 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 (∆H solid ) is the heat lost when one mole of a liquid solidifies at a constant temperature. 17.3

© Copyright Pearson Prentice Hall Heat in Changes of State > Slide 3 of 35 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, ∆H fus = –∆H solid. 17.3

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© Copyright Pearson Prentice Hall Slide 8 of 35 Practice Problems for Sample Problem 17.4 Problem Solving Solve Problem 21 with the help of an interactive guide tutorial.

© Copyright Pearson Prentice Hall Heat in Changes of State > Slide 9 of 35 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? 17.3

Slide 10 of 35 © Copyright Pearson Prentice Hall > 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 (∆H vap ). The amount of heat released when 1 mol of vapor condenses at the normal boiling point is called its molar heat of condensation (∆H cond ). 17.3

© Copyright Pearson Prentice Hall Heat in Changes of State > Slide 11 of 35 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, ∆H vap = –∆H cond. 17.3

Slide 12 of 35 © Copyright Pearson Prentice Hall > Heat in Changes of State Heats of Vaporization and Condensation 17.3

Slide 13 of 35 © Copyright Pearson Prentice Hall > Heat in Changes of State Heats of Vaporization and Condensation 17.3

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© Copyright Pearson Prentice Hall Slide 18 of 35 Practice Problems for Sample Problem 17.5 Problem-Solving Solve Problem 24 with the help of an interactive guided tutorial.

© Copyright Pearson Prentice Hall Heat in Changes of State > Slide 19 of 35 Heat of Solution What thermochemical changes can occur when a solution forms? 17.3

Slide 20 of 35 © Copyright Pearson Prentice Hall > 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 (∆H soln ). 17.3

Slide 21 of 35 © Copyright Pearson Prentice Hall > 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. 17.3

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© Copyright Pearson Prentice Hall Slide 26 of 35 Practice Problems for Sample Problem 17.6 Problem-Solving Solve Problem 26 with the help of an interactive guided tutorial.

© Copyright Pearson Prentice Hall Slide 27 of 35 Section Quiz -or- Continue to: Launch: Assess students’ understanding of the concepts in Section 17.3 Section Quiz

© Copyright Pearson Prentice Hall Slide 28 of 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.

© Copyright Pearson Prentice Hall Slide 29 of The heat of condensation of ethanol (C 2 H 5 OH) is  43.5 kJ/mol. As C 2 H 5 OH condenses, the temperature of the surroundings a.stays the same. b.may increase or decrease. c.increases. d.decreases Section Quiz

© Copyright Pearson Prentice Hall Slide 30 of Section Quiz 3. Calculate the amount of heat absorbed to liquefy 15.0 g of methanol (CH 3 OH) 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  10 3 kJ d.4.75 kJ

© Copyright Pearson Prentice Hall Slide 31 of How much heat (in kJ) is released when 50 g of NH 4 NO 3 (s), moles, are dissolved in water?  s soln =  25.7 kJ/mol a kJ b.13.1 kJ c.25.7 kJ d.1285 kJ 17.3 Section Quiz

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