Expt 10, Thermochemistry
Name:
____________________________
Lab Partner:
_____________________________
Date:
_____________________________
Introduction
Part A
Determination of Heat Capacity of the Calorimeter
Initial temperature of calorimeter and 50 mL cold H2O (Tcold):
Initial temperature of 50 mL warm H2O (Thot) :
___________
___________
Table 1: Time vs temperature data: Heat Capacity of the Calorimeter
[Insert a suitable table here.]
Plot Temp (oC) y vs. Time (s) x. Extrapolate the graph back to the y axis to calculate Tfinal, the final
temperature of the calorimeter and the contents.
Inert the (excel or equivalent) plot showing the extrapolation, don’t forget title, axes labels, units
and trendline.
Calculations
- Heat lost by hot water = heat gained by cold water + heat gained by calorimeter
[comment: note that you assume that the initial temperatures of the calorimeter and of the
cold water are the same.]
- (mL hot water x 1.00 g/mL x ∆Thot x 4.18 J/g oC) = (mL cold water x 1.00 g/mL x ∆Tcold x 4.18 J/g oC) + (∆Tcold x Ccal)
This equation can be rearranged to solve for Ccal the heat capacity of the calorimeter
If you obtain a negative value for Ccal assume that the value of Ccal is zero…..
[…..comment: but, if you do need to assume the heat capacity of the calorimeter is zero, mention
this in the discussion and comment on why you think this assumption was necessary.]
Show all your calculations of Ccal
Part B
Determination of Heat of Neutralization
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NaOH(aq) Molarity: ___________ HNO3(aq) Molarity: ____________
Initial temperature of 50 mL NaOH(aq) and Calorimter (Tb): ___________
Initial temperature of 50 mL HNO3(aq) in grad cylinder (Ta) :
___________
Table 2: Time vs temperature data: Heat of Neutralization
[insert a suitable table here]
Plot Temp (oC) y vs. Time (s) x. Extrapolate the graph back to the time at which the liquids are
mixed to calculate Tfinal the final temperature of the calorimeter and the contents.
Insert the (excel or equivalent) plot showing the extrapolation, units, titles, labels and trendline
equation.
Calculations
∆Tacid = Tfinal - Ta
∆Tbase = Tfinal – Tb
-q neutralization = q solution
q solution = heat gained by acid + heat gained by base + heat gained by calorimeter
q soln = (mL acid x 1.00 g/mL x ∆Tacid x 4.18 J/g oC) + (mL base x 1.00 g/mL x ∆Tbase x 4.18 J/g oC)+ (∆Tbase x Ccal)
Part C
Determination of Heat of Reaction
Mass of CuSO4.5H2O used : ___________ use the analytical balance to weigh approximately 5 g
Mass of Zinc used : ___________ use the analytical balance to weigh approximately 6.5 g
Measure as accurately as possible 95 mL of Distilled Water.
Transfer the CuSO4.5H2O to the 95 mL of distilled H2O in the calorimeter and dissolve completely.
Initial temperature of 95 mL CuSO4.5H2O solution and Calorimter (Tinitial):
2
___________
Add the Zinc to the calorimeter and begin counting time. Continue to measure the temperature at
least 2 minutes after the maximum temperature has been reached.
Table 3: Heat of Reaction
[insert a suitable table here.]
*If your reaction has not reached a maximum temperature after 8 minutes. Stop and
repeat.*
Plot Temp (oC) y vs. Time (s) x. Extrapolate the graph back to the time at which mixing uccurred to
calculate Tfinal the final temperature of the calorimeter and the contents.
Insert the (excel or equivalent) plot showing the extrapolation, trendline, units, titles and axes
labels
Calculations
∆T = Tfinal – Tinitial
= ______________ - ________________
∆T = ____________
Zn(s) + CuSO4(aq) → Cu(s) + ZnSO4(aq) + heat
Note the stoichiometry
- qrxn = heat gained by ZnSO4(aq) (I) + heat gained by Cu(s) (II)+ heat gained by excess Zn(s) (III) + heat
gained by calorimeter(IV)
- qrxn =
(I) + (II) + (III) + (IV)
(IV) Heat gained by calorimeter = Ccal x ∆T = _________oC x ____________J/oC =
(IV) = __________________
(II) Heat gained by Cu(s)
mol of CuSO4.5H2O = mass used _______________ g
x
1 mol
249.69 g
= ___________________ mol*
mol copper produced = _______________ mol
The Heat Capacity of both Copper and Zinc is 25 J/mol oC
Heat gained by copper = __________ mol Cu x 25 J/mol oC x ∆T =
(II) = __________________
(III) Heat Gained by excess Zinc
mol zinc added =
mass used ______________ g
x
3
1 mol
= _______________mol
J
J
65.37 g
mol zinc reacted = mol copper produced =
_______________ mol
moles excess zinc = mol zinc added – mol zinc reacted = _______________mol
Heat absorbed by excess zinc = __________ mol x 25 J/mol oC x ∆T =
(III) = __________________
J
(I) Heat gained by ZnSO4 solution
mol of ZnSO4 produced = mol of CuSO4.5H2O used = _______________mol
Mass of ZnSO4 produced = _______________mol x 161.43 g
1 mol
see * above
= ____________ g ZnSO4
mol water from hydrate (5H2O) = _____________ mol ZnSO4 x 5 = _____________ mol
mass of water from hydrate = ____________mol x 18.02 g
1 mol
= ____________ g H2O from hydrate
Mass of water added to calorimeter = (95) g ___________________ g
Total mass of ZnSO4 solution = _____________ g + ____________ g from hydrate + _____________ g ZnSO4
= _____________ g
Heat gained by ZnSO4 solution = ____________ g x 3.975 J/g oC x ∆T =
(I) = __________________
Therefore qrxn = - [ (I) + (II) + (III) + (IV) ] =
=
_____________
∆Hrxn = ___ qrxn______
mol CuSO4.5H2O
J
J
_____________ kJ
=
_____ __________
kJ/mol
Make sure sign is correct for the exothermic reaction
Discussion
Calculate the actual ∆Ho for the copper/zinc reaction using the data below, compare it to your
result. Calculate your percent error. Comment and include 3 sources of error. You have calculated
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the heat absorbed by the copper and the zinc separately; can you think of a simpler way to get the
same final value?
The standard enthalpies of formation of Zn2+(aq) and Cu2+(aq) from zinc and copper
metals are -152 kJ/mol and 64.4 kJ/mol respectively. Use this data to calculate the ∆Ho the
standard enthalpy of the reaction:
Zn(s) + Cu2+(aq) → Cu(s) + Zn2+(aq)
Conclusion
Summarize the results of all three parts.
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