17.3
Heat in Changes of State
>
Heats of Vaporization and
Condensation
Enthalpy changes accompany changes in state.
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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.
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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.
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SAMPLE PROBLEM 17.4
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SAMPLE PROBLEM 17.4
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SAMPLE PROBLEM 17.4
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SAMPLE PROBLEM 17.4
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Practice Problems for Sample Problem 17.4
Problem Solving 17.21 Solve
Problem 21 with the help of an
interactive guide tutorial.
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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?
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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).
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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.
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17.3
Heat in Changes of State
>
Heats of Vaporization and
Condensation
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17.3
Heat in Changes of State
>
Heats of Vaporization and
Condensation
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SAMPLE PROBLEM 17.5
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SAMPLE PROBLEM 17.5
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SAMPLE PROBLEM 17.5
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SAMPLE PROBLEM 17.5
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Practice Problems for Sample Problem 17.5
Problem-Solving 17.24 Solve
Problem 24 with the help of an
interactive guided tutorial.
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17.3
Heat in Changes of State
>
Heat of Solution
Heat of Solution
What thermochemical changes can
occur when a solution forms?
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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).
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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.
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SAMPLE PROBLEM 17.6
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SAMPLE PROBLEM 17.6
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SAMPLE PROBLEM 17.6
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SAMPLE PROBLEM 17.6
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Practice Problems for Sample Problem 17.6
Problem-Solving 17.26 Solve
Problem 26 with the help of an
interactive guided tutorial.
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17.3 Section Quiz.
Assess students’ understanding
of the concepts in Section 17.3.
Continue to:
-or-
Launch:
Section Quiz
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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.
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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.
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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
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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
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END OF SHOW