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Amanda Diner Mr. Roberts AP Chemistry Periods 2-3 The Hand Warmer Design Challenge Procedure: Part I: 1. The calorimeter calorimeter was assemble assembled d on a magnetic magnetic stirrer stirrer and 100.0 100.0 m o! o! water was was meas"red in a grad"ated cylinder and #o"red into the calorimeter. 2. The tem#era tem#erat"re t"re o! the the water water was was meas"red meas"red and recorded recorded.. 3. A stir stir bar was added added and the stirrer stirrer was t"rned t"rned on so that the the water was stirri stirring ng witho"t witho"t s#lashing. $. %.00g o! Magnesi Magnesi"m "m &"l!ate &"l!ate anhydro"s anhydro"s solid solid was meas"red meas"red and and #"t into into a #lastic #lastic c"#. The magnesi"m s"l!ate was added to the calorimeter while the tem#erat"re was obser'ed. The highest tem#erat"re was recorded. %. The res"lti res"lting ng sol"tion sol"tion was dil"ted dil"ted with with water and dis#osed dis#osed o!. o!. (. The #re'io"s #re'io"s ste#s ste#s were were re#eated re#eated and and the tem#erat tem#erat"res "res were were a'eraged. a'eraged. Part II: 1. A 100.0m 100.0m sam#le sam#le o! water water was #laced #laced in a clean) clean) dry 1%0 m bea*er and and was heated heated with occasional stirring to a##ro+imately %0 degrees Celsi"s. 2. The bea*er bea*er was remo'ed remo'ed !rom !rom the the hot #late #late and #laced #laced on the the lab bench. bench. Meanwhile Meanwhile)) 100 m o! cool water was #laced in the clean) dry calorimeter. 3. The tem#erat"r tem#erat"ree o! the hot water water and the the cold water water was meas"red meas"red and and recorded recorded and then immediately) the hot water was #o"r into the calorimeter. The co'er was ,"ic*ly #"t on. on . $. A!ter 1% seconds seconds the the tem#erat" tem#erat"re re was meas"red meas"red and recorded recorded.. %. The #re' #re'io" io"ss ste#s ste#s were were re#ea re#eated ted again again.. Part III: 1. otes abo"t sa!ety sa!ety were ta*en ta*en on each o! the s"bstan s"bstances ces gi'en. gi'en. 2. The s"bs s"bstan tances ces were were ran*e ran*ed d by thei theirr cost. cost. 3. The ste#s ste#s in Part were !ollowed !ollowed to to determine determine the heat releas released ed by the s"bstance s"bstance.. Prelab Questions: 1. The sodi"m sodi"m and chloride chloride ions were were being se#arated se#arated !rom each each other. other. /ate /aterr molec"les molec"les were s"rro"nding the ions and the water molec"les were se#arating !rom one another. The bonds between the ions were brea*ing) and the bonds between the water molec"les and the hydrogen molec"les were also being bro*en. ew bonds are !ormed between the cations and the anions with the water molec"les. 2. D"ring D"ring this #rocess #rocess)) heat is absorbed absorbed.. The amo"nt amo"nt o! energy energy that it it ta*es to to se#arate se#arate the sodi"m and chloride ions in the str"ct"re and the water molec"les !rom one another is greater than the amo"nt o! energy that is released !rom the ion-water attraction. The di!!erence in the energies o! these two systems is absorbed as heat which ca"ses the water tem#erat"re to decrease.
3. The increase in disorder is thermodynamically !a'orable and an increase in disorder ca"ses dissol"tion to occ"r s#ontaneo"sly e'en tho"g h the reaction is endothermic o'erall. $. The relati'e amo"nts o! energy re,"ired to se#arate the ions in the crystalline lattice solid and released "#on !ormation o! the water-ion attraction in the sol"tion determines the high or low tem#erat"re. ! the energy that is re,"ired to se#arate the ions in the sol"tion is greater) then the heat will be absorbed d"ring the !ormation o! the sol"tion and the sol"tion tem#erat"re will be lower than the starting tem#erat"re and 'ice 'ersa.
Data: Part I:
Cold and ot /ater Tem#erat"res nitial Tem#erat"re
inal Tem#erat"re
Change
ot /ater
$.1
3(.(
-12.%
Cold /ater
23.2
3(.(
13.$
Part II:
Calorimeter Constant Data Mass hot water
100.0
Mass cold water
100.0
nitial tem#erat"re cold
21.2
nitial tem#erat"re hot
%3.0
inal tem#erat"re o! mi+t"re
3(.
Magnesi"m &"l!ate Dissol"tion Data
Part III:
nitial tem#erat"re
20.0
inal tem#erat"re
24.4
n'estigation Data &olid
nitial tem#
inal tem#
aC2352
20.0
2$.
CaCl2
20.0
3(.0
a2C53
20.0
2%.0
aCl
20.0
1.(
iCl
20.0
3.0
$ 53
20.0
12.%
Part IV:
Calorimeter Constant Calc"lations Tem#erat"re change o! hot water 7nthal#y change o! hot water Tem#erat"re change o! cold water 7nthal#y change o! cold water
n'estigation Calc"lations Table 8;ased on Data Abo'e9 &olid
Tem#erat"re change
Thermal energy change in calorimeter contents
Thermal energy change o! calorimeter
nternal energy change
Molar mass
Moles "sed
7nthal#y o! dissol"tion
aC2352
$.
1000
44
-100
2.03
0.0(1
-14.4
CaCl2
1(.0
33%0
2%(
-3(00
111.10
0.0$%0
-0.1
a2C53
%.0
10%0
0
-1130
10(.00
0.0$4
-23.
aCl
-1.$
-20
-22
310
%.
%$0.0(
3.4
iCl
1.0
3440
2
-$0%0
$2.3
0.11
-3$.$
$ 53
-4.%
-1%40
-120
1(0
0.0$
0.0(2
24.0
Post Lab Questions: 1. The !ollowing reactions are e+am#les o! e+othermic reactions. The reason that these are e+othermic reactions is beca"se when the salts are mi+ed with water) heat is generated in the system. /hen the system is gaining heat that means that the reaction is e+othermic. 2. aCl (s) ⟶ a< (aq) < Cl- 8a,9 6 <3.0 *=:mol $ 53 (s) ⟶ $< (aq) < 53- (aq) 6 <2%.$ *=:mol aC2352 (s) ⟶ a< (aq) < C2352- (aq) 6 -14.32 *=:mol a2C53 (s) ⟶ 2a< (aq) < C532- (aq) 6 -2$.0 iCl (s) ⟶ i< (aq) < Cl- (aq) 6 -34.10 *=:mol CaCl2 (s) ⟶ Ca2< (aq) < 2Cl- (aq) 6 -1.%0 *=:mol 3. The changes that occ"rred in these reactions were chemical beca"se the com#o"nds brea* a#art and decom#ose into cations and anions. n order !or these com#o"nd to be bro*en a#art into di!!erent ions) a chemical reaction m"st ta*e #lace to brea* the bonds between the elements. $. This #ost lab ,"estion re,"ires a class set o! data which was not recei'ed) there!ore) a #ro#er #ercent error analysis or a'erage cannot be determined. 5. &ome signi!icant so"rces o! error co"ld ha'e co me !rom the calorimeter. ! the calorimeter was not calibrated correctly) then all o! the calc"lations co"ld ha'e been o!!. Also) the calorimeter was not a 'ery tightly closed system) heat co"ld ha'e easily esca#ed the system and made it di!!ic"lt to obtain acc"rate 'al"es !or the tem#erat"re changes and enthal#y.
