This page intentionally left blank Fundamental constants Quantity Symbol Value Power of ten Units Speed of light c 2.997 925 58* 108 m s–1 Elementary charge e 1.602 176 10–19 C Boltzmann's constant k 1.380 65 10–23 J K–1 Planck constant h 6.626 08 10–34 J s h– = h(cid:2)2p 1.054 57 10–34 J s Avogadro's constant N 6.022 14 1023 mol–1 A Atomic mass constant m 1.660 54 10–27 kg u Mass electron m 9.109 38 10–31 kg e proton m 1.672 62 10–27 kg p neutron m 1.674 93 10–27 kg n (cid:2) Vacuum permittivity e = 1 c2μ 8.854 19 10–12 J–1 C2 m–1 0 0 4pe 1.112 65 10–10 J–1 C2 m–1 0 Vacuum permeability μ 4p 10–7 J s2 C–2 m–1 (= T2 J–1 m3) 0 Magneton Bohr μ = eh–(cid:2)2m 9.274 01 10–24 J T–1 nuclear μB = eh–(cid:2)2me 5.050 78 10–27 J T–1 N p g value of the electron g 2.002 32 e Bohr radius a = 4pe h–2(cid:2)me2 5.291 77 10–11 m 0 0 e Rydberg constant R = me4(cid:2)8h3ce2 1.097 37 105 cm–1 e 0 Standard acceleration of free fall g 9.806 65* m s–2 *Exact value Library of Congress Control Number: 2008934074 Elements of Physical Chemistry, Fifth Edition © 2009 by Peter Atkins and Julio de Paula All rights reserved ISBN-13: 978–1–4292–1813–9 ISBN-10: 1–4292–1813–9 Published in Great Britain by Oxford University Press This edition has been authorized by Oxford University Press for sale in the United States and Canada only and not for export therefrom. First printing W. H. Freeman and Company 41 Madison Avenue New York, New York 10010 www.whfreeman.com Elements Of Physical Chemistry Peter Atkins University of Oxford Julio De Paula Lewis & Clark College Fifth edition W. H. Freeman and Company New York This page intentionally left blank About the book We pay particular attention to the needs of the student, and provide many pedagogical features to make the learning process more enjoyable and effective. This section reviews these features. Paramount among them, though, is something that pervades the entire text: we try throughout to interpret the mathematical expres- sions, for mathematics is a language, and it is crucially important to be able to recognize what it is seeking to convey. We pay particular attention to the level at which we introduce information, the possibility of progres- sively deepening one’s understanding, and providing background information to support the development in the text. We are also very alert to the demands associated with problem solving, and provide a variety of help- ful procedures. Organizing the information Molecular Interpretation icons Ionf optehrefer cwt ogradss ,a tth ae ignitveernn atle emnpeergrayt uorf ea issa mindpele- pendent of the volume it occupies. We can understand this independence by realizing that when a perfect gas expands isothermally the only feature that changes is the average distance between the Checklist of key ideas menoelregcyu rleesm; tahineisr tahvee sraagmee s. pHeoewde avnedr ,t ahse rtehfeorree a troet anlo k iinnetetirc- Although thermo-dynamics mof otlheec ualvaer riangteer asectpioarnast,i othne, stoo ttahle e innetergrnya ils einnedregpye nisd uenn-t Checklist of key ideas changed by expansion. We summarize the principal is a self-contained subject, concepts introduced in each Y(cid:2)ou1 shPohuylsdic naol wc hbeem faimstrilyia ri sw itthhe t hber faonlclohw oinfg c choenmceispttrsy. it is greatly enriched when ECxaalcmulpaltein 2g.2 the change in internal energy chapter as a checklist at the tcohhfa eptmh eyisssttiarcysb laiisnnh det etshr mea nlsad no gdf uetavhgeeel o uopnfs dm tehareltyh iepnmrgin acctoiicpnslce.esp otsf its concepts are explained Nhthuuemtrrmiatinoo dnbyiosntdasym aaircne d ‘is nwytseetre ecmsatn’e. dCc oiannl ostrhiidmee eur tsoeeur sro fho awevnnee rbbgoeyde byn y ac tsoh nea- end of the chapter. We sug- (cid:2)(cid:2)23TWhoer ks taist edso onfe m wahtteenr aar eb ogdays, ilsiq muiodv, eadn da gsoaliinds.t an in terms of atoms and mol- s(tnhtroeun ccdtoeeusdrt srtuehc aottif v ceaalnyn ! e)a xtcphceeorirmim nmeento tde asntoeemr gaey o poneuerts pdouonte . tsSo u 6mp2p2eo akssJeu orienf opposing force. work on an exercise bicycle and loses 82 kJ of energy as gest checking off the box that (cid:2)4Energy is the capacity to do work. (cid:2) ecules. hsoenat?. DWishraetg aisr dt haen yc hmaantgteer ilno sinst beyrn pael resnpeirragtyio onf. the per- (cid:2)5The contributions to the energy of matter are the StrategyThisexampleisanexerciseinkeepingtrackof precedes each entry when you kpionteetnicti eanl eenrgeyrg (yth (eth een eenrgeyrg dyu deu teo tmo optoiosnit)i oann)d. the This icon indicates (cid:2)6The total energy of an isolated system is con- feel confi dent about the topic. served, but kinetic and potential energy may be where we are introducing a molecular interchanged. interpretation. TTable of key equations To see more precisely what is involved in specify- NNotes on good practice ing the state of a substance, we need to define the terms we have used. The mass,m, of a sample is a measure of the quantity of matter it contains. Thus, Table of key equations WWe summarize the most 2 kg of lead contains twice as much matter as 1 kg of SScience is a precise activity lead and indeed twice as much matter as 1 kg of any- The following table summarizes the equations that have been deve iimmportant equations intro- tish itnhge. kTilhoeg rSaymstè(mkge) ,I nwtietrhn a1t ikogn aclu r(rSeIn) tulyn idt eofifn emda asss aand its language should be PPPreaorrtfpieaecl rtpt gyreasss luarwe EppVJq=u=axntJiRpoTn dcdchhueccekdl iisnt ethacaht fcohlalopwtesr tahse a taligaehlrnlbeaot om ymrt saop at( rogsuesr)ss ,ye eow-r svfaih ze eaedsrd mea c s1taea rl Sklmteaègrpvi n=rlue e1snsb ,0il itot3o cauigsknt. sduiod sfute o apP llelayaxr tipmisnr.o euFsrmsoe –rmc iotrayindspvsiiue cniman-l ufufeesaetdu raec ctou rhaetelply e. nWcoe uursaeg teh is Dalton’s law p=pA+pB+... A note on good practiceBe sure to distinguish mass and Virial equation of state p=(nRT/V)(1+nB/V+ cchhapter’s Table of key ideas. windeeigphetn. dMeanst s oisf alo mcaetiaosnu.r eW oef igthhet qisu atnhteit yf oorfc me aettxeerr,t eadn db isy tthhe use of the language and Mean free path, speed, and c=lz an object, and depends on the pull of gravity. An astronaut collision frequency has a different weight on the Earth and the Moon, but the van der Waals equation of state p=nRT/(V−nb)−a(n/V WWhen appropriate, we same mass. pprocedures of science in f Thevolume,V, of a sample is the amount of Maxwell distribution of speeds F(s)=4p⎛⎝⎜⎜2pMRT⎞⎠⎟⎟3/2s2e ddescribe the physical condi- TtVhhr=ee 1eu-0dn0iimtcsme nu3ssiiefo dtnh aetlo ss apemaxcppelr eei sto sco ccvucopuluipemise s1e. 0 (T0whchumisc,3h wo fien s cpwlaurcidteee. ccoonformity to international ttiions under which an equa- cubic metres, m3; cubic decimetres, dm3, or litres, L; ppractice (as specifi ed by millilitres, mL), and units and symbols in general, are ttiion applies. IIUUPAC, the International Union of Pure and Applied Chemistry) and to help avoid common mistakes. Boxes Box 11.2Explosions Where appropriate, we sepa- Aratteh ewrmitha lt eemxpploesraiotunr ies. dIfu teh eto e tnheer grayp riedl einacsreeda sine aonf erexaocthtieorn- Derivations rate the principles from their msoyfi sctt hreeema c rrtaiistoeen s cr, eaasnnundlo ttsth eeisn rce aaap ceftai,o stnhte egr o teerimss efpa esortfae trtu.e rTmeh opefe atrchacetue rrleeear,ac ttaiiononnd FcVaimgno.nl 1=o.t143 6pperWn3eahtperpantr eotw aicnoht o me aoac lehscp uohlteehrsee,r ,e oatfhc ehra codefiu nrsat rde2iu rosfa rnoadnn etd h ovefor etluhfomermee applications: the principles scoh atihne-b rraenacchtiionng geoxepslo seivoennm faasyt oecr.c..ucr awtahsetnro tphheircea lalyre f acshta.i nA- On fi rst reading it might be volume 8Vmolsurrounding the other molecule. branching steps in a reaction, for then the number of chain carriers grows exponentially and the rate of reaction may s are constant; the applications cascade into an explosion. suffi cient simply to appreci- come and go as the subject a2ren HaAisc2nmOti oe( ignxs)a .vb mAeelrpttywhl ecoe ouoemgfn hb ph otlehythdxe r atnoynegpdtee rhnsea aaoscnf tn deioo xontp x yilsyoe gstv eiebonreny,e is2nsi mHfpur2plo(llygev )i,ed +tlehuOdec i 2dmb(ayget )tech→dhe.- ate the ’bottom line’ rather ) DTvaheneri vdmaeotri loWanra v1ao.l1slu emqeu aotfi oan gas described by the pohrnooewg i rnteh seesa epcshr.i nTcchhiaepp lBeteso rxd, eeshsv,eo alwobp oeudt IcTetahx isrpIPern lik roeiotntsriwpaosioatw oiignon na.ncb ttl:riuhoadannetc: a h· HcinH··H·h(HO,gO 22a·· Oi+2++n+s)· ··t··r,(He(O e+O·OpOa2H·22csH→H))t ··→i,co+→→ ·aanOM·nn H·i·sHd OO →l +ie··nH+Oa+vH··d2+oHH2·H OlOv·O tO.(eoH bS2dH r o+a(,ab nma Mrnccaedhhn* iasctnhithngeai-)nptb gtsrha) aenr cechh:ianign Trhaptptc tdchaealv neexl woppormerskes nitohtn roo.f Hu ag ohmw daetevhteaerim,l eadt i- ndeef TsmTt8hhhhVoioseeml we rovvelceoosfcuol luuulrlteemmeh.s ,aT e etoth,h f oeoe trfh r a ve ea4dox Vislcuucpmlslmuoho drlseee,eec r audeeslne x tvo, dc ofsd l uvloruisoad mbtdleuaide≈num cspi4see eVR 43 rVm poimmsof(l2o eo43lcretlupwc)el3ueRclNoe=u3 A=.l8eh .F43 ×aiisprg(d 43uro-p3rsne,rp e i3hs1-)h e.,21 aorr6elrf. in the chapter are currently mathematical development is e- froSmo pfa=r, ntRheT /pVertfoect gas equation of state changes being applied in a variety of modern contexts, an intrinsic part of physical et, p=VnR−Tnb g This equation of state—it is not yet the full van der especially biology and materials science. chemistry, and to achieve full ne Wpualsailosn esq auraet iiomnp—orsthaonut.l dN doetsec trhibaet wa hgeans itnh ew phriecshs urree- il th l il d ithth l vi ABOUT THE BOOK understanding it is important to see how a particu- Visualizing the information lar expression is obtained. The Derivations let you acudrjuresnt tt hnee eledvse, la onfd d metaakile t ihta eta ysoieur rtoeq rueivriee wto myoauterr ial. Artwork Temperature All the calculus in the book is confi ned within these In many instances, a concept Derivations. is easier to understand if it is Easn ehregayt presented in visual, as well as Fig. 2.14The loss of energy into the surroundings can be written, form. Every piece of dperotecectsesd p broyc neoetdinsg. whether the temperature changes as the FFurther information artwork in this new edition Further information 1.1 One way to measure the energy transferred as heat Kinetic molecular theory IInn some cases, we have has been carefully rendered icincoa nals ppisrrtooscc oeefss ssa oicsco tcnout ruasisneae art chinae lrwomrhioimcmhee ttetherer( Fraeinga.cd t2ia.o1ns4u o)r,rr w opuhhniycdsh- Oabnilei tyo ft ot htue rne sssiemntpilael, qskuialllsit aotfiv ea idpehayss iicnatlo crhigeimd,i stte sitsa bthlee, jjuudged that a derivation is in full colour, to help you quantitative theories. The kinetic model of gases is an esextc oelulet nint etxhaem tepxlet aonf dth tius rtnecs htnhieqmu ei,n atos ipt rteackieses tehxep creosnscioepntss. ttooo long, too detailed, or master the concepts presented. As usual in model building, there are a number of steps, but elyaicnhg opnhey issi cmalo ptiivcatuterde, biny ath cilse acar saep ap rsewciaartmio no fo mf tahses upnodinerts- ttooo different in level for it in ceaseless random motion. The key quantitative ingredi- ents we need are the equations of classical mechanics. So we begin with a brief review of velocity, momentum, and ttoo be included in the text. In NeTwhteo nve’sl osceictoyn, dv, l aisw a ovfe mctoorti,o an q.uantity with both magni- Living Graphs tude and direction. The magnitude of the velocity vector is tthhese cases, the derivations ztvh-za,e x aserpsee, etdhre,e s vpc,o egcmitvipveoneln ybe yn( tvFsi =go.(f v 1tx2h.2+e0 vv)ey2. c+Ttovhrz2e )a 1lm/o2,na wggn htihetruee d xve-x ,,oyvf-y ,,e aaanncddh aare found less obtrusively at IInn some cases, the trends mwceoxiomatmhmpemponlnaeteu,gnmnt|iv,,t uxipt|d,s e omvfpae ala=u npesma wrvtthiictehNl eo emouwfta tmgaon nasi’sitsgsu ndsm,ee c iiosso ndtfdh eevnl xaov.wet ecTdtoo hf|re. m. p.l|oi.=n tFimeooanvrr tthhe end of the chapter. Number of molecules Lteomwperature High oatoatee rgr pprarrepothp w earhrteiee n sd tpihfrfiee c sguernlatt pteohd iiinsn - temperature vviewed as a static fi gure. In Speed Mathematics support Fig. 1.8The Maxwell distribution of speeds and its variation ssuuch cases, a dynamic Liv- with the temperature. Note the broadening of the distribution and the shift of the rms speed to higher values as the tem- perature is increased. iinng graph is available in the itnhtee rmAocltaivr imtyas(as) cPolonts dtaifnfet raetn t1 d0i0s tgri bmutoiol−n1sa bnyd kveaerpyiinngg t(bh)e Utesme pmeraatthuerme aotfi ctahle ssoafmtwpalere b oert wtheee nL 2iv0in0g K garnadp h20a0p0p leKt. eeBBook version of the text. Bubbles forfo mmo tlheecu tleexst w’s itwhe sbp eseitdes t oin ethvael uraanteg en 1u0m0e mric sa−ll1yt toh 2e0 f0ra mct iso−n1 at 300 K and 1000 K. (c) Based on your observations, provide AALiving graph can be used sea level, given that 100.0g of a2ir c2onsists of 75.y5 g of a molecular interpretation of temperature. You often need to know how iNn2g, e2a3c.2h gm oafs Os t2o, aannd a 1m.3o ugn otf i nA rm. Holienst:.Begin by convert- ttoo explore how a property [Answer:0.780, 0.210, 0.009] to develop a mathematical cchhanges as a variety of pa- expression, but how do you theF opra rat iaml ipxrteusrseu roef opfe Jr fewcitt hg atshees ,c ownet rcibaunt iiodne ntthifayt rameters are changed. J makes to the total pressure. Thus, if we introduce go from one line to the next? p=nRT/Vinto eqn 1.7, we get The fi gures in the book with associated Living A green ‘bubble’ is a little pJ = xpJp= n=R Tx/VJ ×nRVT=nnxJJ×RVT=nJ×RVT graphs are fl agged with icons in the fi gure legends as Definition rtieomni nudseedr ,a tbhoeu atp tphreo sxuibmsatittiuo-n f TinTsJh htoaehf te v Ji as pw,l urtoeheus eosl udpf r aneerxJ tRoeiarfTlt /JpiV nrue tissshes eduth roieetn hop eDfrr eJwas alsitusso erdn eee’ smfit hnlpaaettwdy a ,bc noyp anreomtqavnoiin du1een.rd7t. shown here. all the gases in the mixture behave perfectly. If the made, the terms that have geqasne s1 a.7r,e froera lt,h tahte idr epfianrittiiaoln p raepspsulireess taor ea lslt iglla gseivse, na nbdy the sum of these partial pressures is the total pres- been assumed constant, and sure (because the sum of all the mole fractions is 1); Thermocouples Animations so on. A red ‘bubble’ is a Sample Reference reminder of the signifi cance of an individual term in In some cases, it is diffi cult an expression. to communicate a dynamic Heaters A differential scanning calorimeter. The sample and a refer- process in a static fi gure. In epnarctem emnattse. rTiahle a oreu tphueta itse tdh ein d isffeepraernactee ibnu pto wideenr tniceaeld ceodm to- maintain the compartments at equal temperatures as the tArha tebe r racietoefn cscotoanmnsttm aonfet ntohtfe a Tc hgoreBrornueegsrphakolo rfnu[oBdtr iw]tnhgais rrd ec rhveeaaprcstteeio r rnwe aaecn tdwio krnit′r.e fWo krr htfheoenr AA brief comment svuercshi oinnsst aonf cseesle, catnedim aarttewdo rk temperaturSinee treeisr aaencst. iavnei mebaoteodk .version of this figure in the AiaC rtfehoserwpreea cradtrie va esnledyv. reervael srsteep rsa tae, bc,o .n.s. tiann at sm keac,hkab,n .is.m.a,n wd ek wa′,rkitb′e, t.h..e, AA topic often needs to draw are available in the eBook For instance, we could envisage this scheme as the oon a mathematical proce- version of the text. Where interconversion of coiled (A) and uncoiled (B) DNA emnoclee couf lietss. rTathees noeft froartme aotfi ofonr amnadt idoenc oomf Bp,o tshitei odnif,f eisr- ddure or a concept of physics; animated versions of fi gures are available, these are Net rate of formation ofB =kr[A]−k′r[B] AA brief comment is a quick fl agged in the text as shown below. When the reaction has reached equilibrium the cthoenrcee nistr antoio nnse to ff oArm aantdio Bn aorfe e[iAth]eeqr asnudb s[tBa]neqcea. nIdt rreeminder of the procedure follows that kr[A]eq=k′r[B]eq oor concept. dh f h h ilibi f h ABOUT THE BOOK vii Problem solving Discussion questions Questions and exercises Discussion questions The end-of-chapter mate- 2.1Discuss the statement that a system and its surround- A brief illustration same mass. ibnogusn daarery dthisattin sgeupisahraetde sb tyh esmpe.cifying the properties of the Thevolume,V, of a sample is the amount of rial starts with a short set of 2.2What is (a) temperature, (b) heat, (c) energy? A brief illustration is a short TtVhhr=ee 1eu-0dn0iimtcsme nu3ssiiefo dtnh aetlo ss apemaxcppelr eei sto sco ccvucopuluipemise s1e. 0 (T0whchumisc,3h wo fien s cpwlaurcidteee. questions that are intended 22..34PArroev tidhee mlawol eocfu claorn insetervrparteiotnat ioofn esn feorrg wyoinrk daynnda hmeiacts. and cubic metres, m3; cubic decimetres, dm3, or litres, L; the First Law of thermodynamics identical? example of how to use an mreivlileilwitreeds ,i nm ALp),p aenndd iuxn 1it.s and symbols in general, are to encourage refl ection on the 2co.5nsEtaxnptla pinre tshseu rdeif afenrde wncoer kb oeft wreeveenrs eibxlpea enxspioann swioonr ka nadg athinesirt eitniqctuuraolatdiro,u wnce etdh s aihnto htwhae sh tjoeuwxstt . tb oIen ue pnsea r- sdco1Atooiafe.rm 0 sb1fc10iep0unr.0 il0b×iyet10 ii cc1fo0 r m ×e0n0idlp− le3(11uclicani0msdsic −m tmtte43hrh eai3mte=s.tht rsi3cee1o.aa s0fmnTs r0(eaole ic, t( drt1aB1eioso00es n−−oct)12, hna oumeudefss sm e)teee.hx ) Te13p1s,h ri cumceuwmnmsspihs,t l = ieet=c(osd h11u u c 0a0ncios−s−ih1tn 21 tvdacm0hesom0er ,n c t ,(av 1sm1i ena0v0)r m−o ws02bli ueoyhmcm n imcia)ts3ehss3,, mbtaraiontaeedrdie abrl y ca osnondlt vetixont gv t ihneawunm i ites ir noic baa- l (c2ep2eco..nrx)67onpeCcsrrESeepge,ssxpmyqssp eua−.ilcoaeniCnifndnyscV t,:etmh ahse(ne=.a d )cR d hq.ieaffnxe=pgrleean niinRnc Te et hnblneteh( tVawliflmp/eVyeii t)noa; t fi (toabhn )ecs hD ceHohmfa ni=ctghaelDe o Uinrf o pi+lnhlotywepsrDiincnVaag;ll data and how to manipulate tinemtTrophdeer uoacttthuioerren ,p, arfoonprd e eravtmieenos uwthneot huoagfvh es utmhbeesynta tmniocaneye) dbn e(ep efrdae msmsiuloirareer, problems. EAsxseurmceis aell sgases are perfect unless stated otherwise. units correctly. ffroorm us eev ienr yscdiaeyn clief.e, they need to be defined carefully 2th.1rouCgahlc (ual)a 1te.0 tchme 3,w (bo)r k1 .0d odnme3 abgya ian sgt aasn awtmheons piht eerixcp parnedss- Exercises WWorked examples The core of testing understanding is the collection of Example 2.2 Calculating the change in internal energy EEachWorked example has end-of-chapterExercises. At the end of the Exercises Nutritionists are interested in the use of energy by the human body and we can consider our own body as a thermodynamic ‘system’. Calorimeters have been con- aaStrategy section to suggest you will fi nd a small collection of Projects that bring structed that can accommodate a person to measure (nondestructively!) their net energy output. Suppose in the course of an experiment someone does 622 kJ of hhow to set up the problem together a lot of the foregoing material, may call for work on an exercise bicycle and loses 82 kJ of energy as heat. What is the change in internal energy of the per- son? Disregard any matter loss by perspiration. ((aanother way might seem the use of calculus, and are typically based on mate- StrategyThis example is an exercise in keeping track of signs correctly. When energy is lost from the system, w orqis negative. When energy is gained by the system, mmore natural: setting up rial introduced in the Boxes. worqis positive. S(6o2lu2t kioJn is Tloos tta bkye dnooitneg o wf othrke) saingdn sq w=e− 8w2r ikteJ (w82= k−J6 i2s 2lo ksJt pproblems is a highly per- by heating the surroundings). Then eqn 2.8 gives us DU=w+q=(−622 kJ) +(−82 kJ) =−704 kJ ssoonal business) and use or We see that the person’s internal energy falls by 704 kJ. Later, that energy will be restored by eating. A note on good practiceAlways attach the correct fifi nd the necessary data. Then signs: use a positive sign when there is a flow of energy into the system and a negative sign when there is a flow of energy out of the system. tthhere is the worked-out Self-test 2.4 AAnswer, where we empha- An electric battery is charged by supplying 250 kJ of energy to it as electrical work (by driving an electric current through it), but in the process it loses 25 kJ ssiize the importance of using of energy as heat to the surroundings. What is the change in internal energy of the battery? [Answer:+225 kJ] uunits correctly. Self-tests EachWorked example has a Self-test with the an- swer provided as a check that the procedure has been mastered. There are also a number of free- standingSelf-tests that are located where we thought it a good idea to provide a question to check your understanding. Think of Self-tests as in-chapter Ex- ercises designed to help you monitor your progress. The Book Companion Site The Book Companion Site provides teaching and learning resources to augment the printed book. It is free of charge, complements the textbook, and offers additional materials which can be downloaded. The resources it provides are fully customizable and can be incorporated into a virtual learning environment. The Book Companion Site can be accessed by visiting http://www.whfreeman.com/elements5e For students For lecturers Answers to exercises Artwork The fi nal answers to most end-of-chapter exercises A lecturer may wish to use the illustrations from are available for you to check your work. this text in a lecture. Almost all the illustrations are available in PowerPoint® format and can be used for lectures without charge (but not for commercial Web links purposes without specifi c permission). Links to a range of useful and relevant physical chemistry web sites. Tables of data All the tables of data that appear in the chapter text are available and may be used under the same condi- tions as the illustrations. On-line quizzing New for this edition, on line quizzing available on the book companion site offers multiple-choice questions for use within a virtual learning environ- ment, with feedback referred back to relevant sec- tions of the book. This feature is a valuable tool for either formative or summative assessment.