001
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`General
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`; ‘. BROOKS/COLE
`I6 CENGAGE Learning
`
`General Chemistry Enhanced Edition,
`Ninth Edition
`
`Darrell D. Ebbing, Steven D. Gammon
`
`Publisher: Charles Hartford
`
`Assistant Editor: Stephanie VanCamp
`Editorial Assistant: Jon Olafsson
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`Amherst)
`Production Service: Pre-PressPMG
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`Compositor: Pre-PressPMG
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`Cover photo 0 Philip Evans 2007
`
`Credits: A list of credits precedes the index.
`
`Warning: This book contains descriptions of
`chemical reactions and photographs of
`experiments that are potentially dangerous
`and harmful if undertaken without proper
`supervision. equipment. and safety
`precautions. Do NOT attempt to perform
`these experiments relying solely on the
`information presented in this text.
`
`O 2011. 2009 Brooks/Cole. Cengage Learning
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`pCflIl!|i0O|f¢QtlQlI.¢Q0'l[¢.¢OI'I
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`Library of Congress Control Number: 2009939580
`lSBN-13: 978-0-538-49752-7
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`003
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`003
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`

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`488 I Solutions
`
`rtourte 12.13 D
`
`lnstanlotuilooldconpresspocts
`Theinner bag ol the instanthotcompress
`contairs caldum chloride, CaCl,. When the
`inner bag is broken, the CaCl. dissolves
`emthermically in water (heat is released).
`The instant cold compress contains an inner
`bag of ammonium nitrate, NH.N0,, which
`when broken apart allows the NH.NO, to
`dssolve II'l the water In the outer bag. The
`solution process is endothermic (heat is
`absorbed). so the bag leels cold.
`
`Piston
`
`Gaseous C03
`
`of CO,
`
`
`Aqueous solution
`
`FIGURE l2.M A
`
`Effect at pressure on gas solublly
`when the piston is pushed down, increasing
`the partial pressure of carbon dioxide, more
`gas dissolves (which tends to reduce the
`carbon tioxide panial pressure).
`
`
`
`increase with rising temperature. For example. potassium nitrate. KNOJ. changes
`solubility dramatically from I4 g/I00 g H20 at 0°C to 24$ gll00 g H20 at
`l00°C.
`Copperlll) sulfate. CuSO,.. shows a moderate increase in solubility over this
`temperature interval. Sodium chloride. NaCl. increases only slightly in solubility with
`temperature.
`A number of ionic compounds decrease in solubility with increasing temperature.
`Calcium sulfate. CaS0,.. and calcium hydroxide. Ca(OH);. are common examples.
`They are slightly soluble compounds that become even less soluble at higher temper-
`atures. Cerium selenate. Ce;(Se0,)_1. shown in Figure l2.l2. is very soluble at 0°C
`but much less soluble at
`l00°C.
`Heat can be released or absorbed when ionic substances are dissolved in water.
`
`
`
`In some cases. this heat of solution is quite noticeable. When sodium hydroxide is
`dissolved in water. the solution becomes hot (the solution process is exothermic). On
`the other hand. when ammonium nitrate is dissolved in water, the solution becomes
`very cold (the solution process is endothermic). This cooling effect from the dissolv-
`ing of ammonium nitrate in water is exploited in instant cold packs used in hospitals
`and elsewhere. An instant cold pack consists of a bag of NH,.,N0, crystals inside a
`bag of water (Figure l2.I3). When the inner bag is broken. NI-|,.NO_. dissolves in the
`water. Heat is absorbed. so the bag feels cold. Hot packs. by contrast. containing either
`CaCl2 or MgS0,,. dissolve in water with the evolution of heat.
`
`lroutrrecnqo
`
`In general. pressure change has little effect on the solubility of a liquid or solid in
`water. but the solubility of a gas is very much affected by pressure. The qualitative
`effect of a change in pressure on the solubility of a gas can be predicted from Le
`Chatelicr’s principle. Ln Chlfliofs principle states that when a system in equilibrium
`is disturbed by a change of temperature. pressure. or concentration variable. the sys-
`tem shifts in equilibrium composition in a way that tends to counteract this change
`of variable. Let us see how Le Chatelier‘s principle can predict the effect of a change
`in pressure on gas solubility.
`Imagine a cylindrical vessel that is fitted with a movable piston and contains car-
`bon dioxidc gas over its saturated water solution (Figure l2.l4). The equilibrium is
`
`C02(g) : CO;(aq)
`
`Suppose you increase the panial pressure of CO; gas by pushing the piston down. This
`change of partial pressure. according to Le Ch5telier‘s principle. shifts the equilibrium
`
`Copyright 2010 Ccngage Learning. Inc. All Rights Reserved. May not be copied. scanned. or duplicated. in whole or in part.
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`004
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