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1、第四章材料化學(xué)熱力學(xué)Chapter4ChemicalThermodynamicsofMaterials1.Cs熔體的標(biāo)準(zhǔn)吉布斯自由能(單位為J)與溫度T(單位為K)的關(guān)系為ΔGom,Cs=2100-6.95T,求Cs的熔點(diǎn)。RelationshipbetweenthestandardGibbsfreeenergy(inunitsofJ)ofCsmeltandtemperatureT(K)isshownasΔGom,Cs=2100-6.95T,pleasedeterminethemeltingpointofCs.解:根
2、據(jù)熱力學(xué)定律,當(dāng)ΔG<0時(shí),反應(yīng)可以自發(fā)進(jìn)行,因此ΔG=0時(shí)對(duì)應(yīng)的平衡反應(yīng)(即Cs由固相轉(zhuǎn)變?yōu)橐合嗟姆磻?yīng))的溫度即為Cs的熔點(diǎn)。由ΔGom,Cs=2100-6.95T=0,可得T=302K,所以Cs的熔點(diǎn)為302K。Answer:Accordingtothelawsofthermodynamics,whenΔG<0,thereactioncanbespontaneous.Therefore,ΔG=0correspondingtotheequilibriumreactionofCschangefromsolidphas
3、eintoliquidphase,thetemperaturecorrespondingtothemeltingpointofCs.FromΔGom,Cs=2100-6.95T=0,wecangetT=302K,sothemeltingpointofCsis302K.2.通過(guò)埃靈罕姆圖解釋為何碳在高溫下可以用作金屬氧化物的還原劑。AccordingtotheEllinghamdiagram,pleaseexplainwhythecarboncanbeusedasareductantofthemetaloxidesat
4、hightemperature.答:根據(jù)埃靈罕姆圖,ΔGo-T曲線越在下方,氧化物的ΔGo負(fù)值越大,其穩(wěn)定性就越高。所以在給定的溫度下,位于下方的ΔGo-T曲線所對(duì)應(yīng)的元素可使位于上方曲線的金屬氧化物還原。由埃靈罕姆圖還可知,CO生成線的斜率為負(fù),隨著溫度升高,ΔGo越負(fù),CO穩(wěn)定性越高。而金屬氧化物的生成線的斜率都為正,隨著溫度升高,ΔGo越正,氧化物穩(wěn)定性越低。所以,碳在高溫下可以用作金屬氧化物的還原劑。AccordingtotheEllinghamdiagrams,thelowerthesiteofΔGo-Tc
5、urve,thebiggerthenegativevalueofΔGo,themorestablethemetaloxide.So,atagiventemperature,theelementofthebelowΔGo-TcurvecanreducethemetaloxideoftheaboveΔGo-Tcurve.WecanseethattheslopeofCOformationlineisnegative,andwiththeincreaseoftemperature,ΔGobecomesmorenegative
6、,indicatesthatCOismorestable.However,theslopesofmetaloxidesformationlineareallpositive,withtheincreaseoftemperature,ΔGobecomesmorepositive,indicatesthatmetaloxideismoreunstable.Therefore,thecarboncanbeusedasareductantofthemetaloxidesathightemperature.3.(a)對(duì)任何反應(yīng)
7、,請(qǐng)說(shuō)明ΔG和ΔGo為0的意義;(b)對(duì)于“如果反應(yīng)的ΔGo是正值,則反應(yīng)不會(huì)如反應(yīng)式所寫的那樣向右進(jìn)行”的說(shuō)法,談?wù)勀愕挠^點(diǎn)。(a)foranyreaction,pleaseindicatethesignificanceofΔG和ΔGo;(b)For“ifΔGoofareactionispositive,thereactionwillnotgoalongasthereactivewritten”,talkaboutyouropinion.答:(a)對(duì)于任何反應(yīng),ΔG(吉布斯自由能變化)是描述一個(gè)化學(xué)反應(yīng)的驅(qū)動(dòng)力,即
8、可據(jù)此判斷反應(yīng)發(fā)生的可能性。根據(jù)熱力學(xué)第二定律可知,“在任何自發(fā)變化過(guò)程中,自由能總是減少的”。所以,ΔG為0說(shuō)明反應(yīng)過(guò)程處于平衡狀態(tài)。而ΔGo為標(biāo)準(zhǔn)吉布斯自由能變,即物質(zhì)處于標(biāo)準(zhǔn)狀態(tài)時(shí)((指定溫度(273.15K)和壓力(101.325KPa))的生成自由能。(b)已知ΔGo=-RTLnK,若ΔGo為正值,則LnK必需為負(fù)值,則K<1,表明反