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AP#Chemistry#Lab:#Determination#of#the#Molar#Heat#of#Fusion#for#Water#and#Heat#of#Solution#of#a# Solid# ! Introduction#to#Thermochemistry#&#Heat:! Thermochemistry! is! one! area! of! chemistry! dealing! with! the! quantitative! analysis! of! heat! absorbed! or! evolved!by!physical!and!chemical!processes.!Heat!(q)!can!be!defined!as!the!flow!of!energy!into!and!out!of!a! system!due!to!a!temperature!difference!between!the!thermodynamic!system!and!its!surroundings.! Heat! energy! will! flow! from! the! region! of! higher! temperature! to! the! region! of! lower! temperature! until! thermal!equilibrium!has!been!reached.!At!thermal!equilibrium,!the!temperature!of!the!two!regions!will!be! equal!at!any!one!time.! Heat!&!temperature!are!both!measures!of!kinetic!energy!but!heat!measures!total!energy!and!temperature! measures!the!average!energy.!For!example,!if!you!had!a!teaspoonful!of!boiling!water!versus!a!cup!of!boiling! water!(both!at!100oC),!the!cup!of!boiling!water!would!be!more!painful!to!spill!on!your!hand!because!it!has! more!heat!(total!energy).! The!formula!for!heat!is!as!follows:!q!=!smΔt!Where!q!=!heat,!s!=!specific!heat,!m!=!mass,!Δt!=!change! in!temperature.!(the!specific!heat!for!water!=!4.184!J/goC.)! ! Introduction#to#Heat#of#Fusion:! The!heat!needed!to!melt!1!mole!of!a!pure!substance!is!called!the!heat!of!fusion!and!denoted!as!ΔHfus.!To! melt!a!pure!substance!at!its!melting!point!requires!an!extra!boost!of!energy!to!overcome!lattice!energies.! The!heat!of!fusion!(ΔHfus)!can!be!calculated.!At!constant!pressure,!the!heat!exchanged!is!equal!to!the!heat! of!fusion:! ! qp!=!ΔHfus.! ! Procedure#for#the#Molar#Heat#of#Fusion#of#Water:# 1)! Place!about!400!–!500!mL!of!deionized!water!into!a!600!mL!beaker!and!place!onto!a!hotplate.! a.! Heat!up!the!water!to!between!60oC!and!70oC.! 2)! Obtain!the!mass!of!two!clean!and!dried!empty!Styrofoam!cups!with!the!top.! a.! These!two!cups!should!be!stacked!on!top!of!one!another!and!the!top!should!have!a!hole!in!it! to!facilitate!the!use!of!your!thermometer.! 3)! Add!enough!warm!water!to!the!pre–weighed!set!of!cups!to!fill!between!65–75%!full.! 4)! Obtain!the!mass!of!the!set!of!cups!containing!the!warm!water!with!the!cap!on!top.! a.! Ensure!that!no!water!is!clinging!to!the!outside!walls!of!the!Styrofoam!cups.! 5)! Measure! the! temperature! of! the! warm! water! to! the! nearest! tenth! to! hundredth! of! a! degree! depending!on!the!thermometer!calibrations!(0.1oC!–!0.01oC).! 6)! Immediately!following!this!measurement,!add!enough!ice!to!cover!the!surface!of!the!water.! a.! Ensure!that!you!do!not!allow!any!of!the!warm!water!to!splash!out.! 7)! Replace!the!top!and!gently!stir!the!mixture!with!the!thermometer.! 8)! Once!the!ice!has!melted!and!the!temperature!has!stabilized,!record!the!final!temperature!of!the! cool! water! to! the! nearest! tenth! to! hundredth! of! a! degree! depending! on! the! thermometer! calibrations!(0.1oC!–!0.01oC).!! 9)! Following!this!measurement,!remove!the!thermometer!and!record!the!mass!of!the!cool!water!in! the!set!of!cups!with!the!top.! 10)! Repeat!this!experiment!(steps!1!–!9)!for!a!second!trial.! ! Clean#–#Up:! 1)! All!water!and!salt!solutions!can!be!disposed!of!down!the!sink.! ! ! ! ! ! Sample#Data#Table#for#the#Molar#Heat#of#Fusion#of#Water:! a)!Mass!of!Styrofoam!cups!with!top!in!grams:!! ! Trial!1:!________!Trial!2:!________!! b)!Mass!of!Styrofoam!cups!with!top!plus!warm!water!in!grams:!! Trial!1:!________!Trial!2:!________! c)!Mass!of!warm!water!in!grams!(b!–!a):! ! Trial!1:!________!Trial!2:!________!! d)!Stable!temperature!of!warm!water!in!oC:! ! Trial!1:!________!Trial!2:!________! e)!Stable!temperature!of!warm!water!in!Kelvin:! ! Trial!1:!________!Trial!2:!________! f)!Stable!temperature!of!cool!water!in!oC:! ! Trial!1:!________!Trial!2:!________! g)!Stable!temperature!of!cool!water!in!Kelvin:! ! Trial!1:!________!Trial!2:!________! h)!Temperature!change!of!warm!water!in!oC!(f!–!d):!! ! Trial!1:!________!Trial!2:!________! i)!Mass!of!Styrofoam!cups!with!top!plus!cool!water!in!grams:!! Trial!1:!________!Trial!2:!________! j)!Mass!of!cool!water!in!grams!(i!–!a):! ! Trial!1:!________!Trial!2:!________!! k)!Mass!of!ice!in!grams!(j!–!c):!! ! Trial!1:!________!Trial!2:!________! l)!Amount!of!heat!lost!(in!Joules)!by!the!warm!water†:!! † q = (c)(4.184 J/g • oC)(h) ! Trial!1:!________!Trial!2:!________!! m)!Amount!of!heat!gained!(in!Joules)!by!the!ice‡:!! ‡q = (k)(4.184 J/g • oC)(f–0.00oC) ! Trial!1:!________!Trial!2:!________!! n)!Amount!of!heat!(in!Joules)!that!melted!ice!(|l|!–!|m|):! ! Trial!1:!________!Trial!2:!________! o)!Experimental!heat!of!fusion!(in!Joules/gram)!of!water!(n/k):! ! Trial!1:!________!Trial!2:!________!! p)!Experimental!molar!heat!of!fusion!(in!Joules/mole)!of!water!(o•MW):! ! Trial!1:!________!Trial!2:!________! q)!Experimental!molar!heat!of!fusion!(in!kilojoules/mole)!of!water!(p/1000):! ! Trial!1:!________!Trial!2:!________! Average:!________! r)!True!molar!heat!of!fusion!(in!kilojoules/mole)!of!water!*:!_____________! s)!Percent!error!for!molar!heat!of!fusion!of!water:!_____________! ! Reference!for!true!molar!heat!of!fusion!for!water:! __________________________________________________________! ! ! * You must look up this value online or in a text & properly reference. ! # # # # # # # # Lab#Report:! •! Title!Page! •! Summary!! a.! Purpose! b.! Compare!the!true!and!experimental!heat!of!fusion!of!water.!!Include!percent!error.! •! Introduction! a.! Discuss!thermochemistry!and!heat!background.! •! Results!and!Discussion! a.! Discuss!your!procedure!with!the!data!you!collected.!! b.! Determine!the!molar!heat!of!fusion!of!water.!! c.! Compare!experimental!results!with!the!true!values!&!determine!the!percent!error!in!each! experiment!using!the!following!formula:! i.! [(true!value!–!experimental!value)/true!value]!*!100%! ii.! Error!cannot!be!negative;!take!the!absolute!value!if!necessary.! d.! Discuss!all!reasons!for!error.! e.! Include!your!data!tables.! f.! Show!all!calculations.! •! Conclusion! a.! Summarize!the!major!points!of!your!experiment.! # !