The Meaning of a Chemical Equation：一个化学方程式的意义.doc

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1、TheMeaningofaChemicalEquationChemicalequationsgiveinformationinthreemajorareas.1.Theytelluswhatsubstancesarereacting(thosebeingusedup)andwhatsubstancesareproducts(thosebeingmade).2.Thecoefficientsofabalancedequationtellusinwhatratiothesubstancesreactorareproduced.3.There

2、lativeamountsofoilsubstancesinvolvedinthereaction.Thislastpointhaspracticalconsequenceswheneverchemicalsreact.Forexample,thelargemiddletankofthespaceshuttleactuallyhastwosmallertanksinit-oneholdingliquidoxygenandtheotherholdingliquidhydrogen.Thetankwiththehydrogenholdstw

3、iceasmuchastheoxygen-holdingtank.Why?Answer-hydrogenandoxygenreactina2:1ratio.Foranyofoxygenusedbytheshuttie,twiceasmuchhydrogenisneeded.Ifthetwotankswereequalsizes,thehydrogentankwouldrundrywhentheoxygentankwasstillhalf-filled.Thereactantsareontheleftsideofachemicalequa

4、tionandtheproductsareontherightside.However,youmightask,"Ontheleftandrightsideofwhat?"Answer-thearrow.2H2+O2—>2H2OOntheleftsidearethereactants-hydrogenandoxygen.Wewillignorethetwoinfrontofthehydrogenforamoment.Ontherightsideistheproduct-water.Wewillalsoignorethetwoinfron

5、tofthewater,butwewillsoonreturnto汁.Pleasebeawarethattherecanbeone,two,three,ormoresubstancesoneithersideofthearrow,asinthismorecomplexequation：Ca(H2PO4)2+CaSO4+HF—>CaioF2(P04)6+H2SO4Typicallythearrowisreplacedwith"produces"or"yields"whentheequationissaidoutloud.Coefficie

6、ntsarethenumbersinfrontoftheformulas.Hereistheexampleequationagain：2H2+O2—>2出0Notethepresenceofatwoinfrontofthehydrogenandalsothewater.Thesearecalledthecoefficients.Thesenumbersgivetwoveryimportantpiecesofinformationabouttheequation.Youmustunderstandbothinordertoreadandt

7、ousechemicalequationssuccessfully.First：thecoefficientsgivethenumberofmolecules(oratoms)involvedinthereaction.Intheexamplereaction,twomoleculesofhydrogenreactwithonemoleculeofoxygenandproducetwomoleculesofwater.Second：thecoefficientsgivethenumberofmolesofeachsubstanceinv

8、olvedinthereaction.Intheexamplereaction,twomolesofhydrogenreactwithonemoleofoxygenandproducetwomolesofw