Enthalpy Changes
Aims
To measure the enthalpy change of the reaction between copper (II) sulphate
and zinc.
Scientific principles involved in the practical work
Enthalpy change is the heat change accompanying a chemical reaction at
constant volume or constant pressure. The enthalpy change tells the amount
of heat absorbed or evolved during the reaction. It is denoted by ∆H where
enthalpy change of exothermic reaction will be in negative and endothermic
reaction will be in positive.
Zinc and copper ion proceed redox reaction where zinc is in higher position of
reactivity series than copper. Hence, zinc is more likely to lose electrons,
proceed oxidation and copper ion will gain electrons, proceed reduction.
Redox Equation: Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
Overall Equation: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
Method
1. Pipette 25.0cm3 of the copper (II) sulphate solution into the polystyrene cup.
2. Weight about 6g of zinc powder in the weighing bottle - as this is an excess,
there is no need to be accurate.
3. Put the thermometer through the hole in the lid, stir, and record the
temperature every half minute for 21/2 minutes in the table below.
4. At precisely 3 minutes, add the zinc powder to the cup.
Yuki Wong Yee Kee
Student No. 10782321
PPS
5. Continue stirring, and record the temperature for an additional 6 minutes in
the table below.
Results and Calculations
Time (minutes)
0.0
0.5
1.0
1.5
2.0
2.5
Temperature (℃)
18.7
18.7
18.7
18.7
18.7
18.7
Time (minutes)
5.0
5.5
6.0
6.5
7.0
7.5
Temperature (℃)
48.8
47.7
46.7
45.6
44.6
43.8
3.0
3.5
4.0
4.5
51.2
50.8
49.8
8.0
8.5
9.0
9.5
43.1
42.2
41.3
40.4
not
done
Yuki Wong Yee Kee
Student No. 10782321
PPS
m = mass of solution
= 25 g
C = specific heat capacity of water
= 4.18 Jg-1K-1
Initial temperature = 18.7 ℃
Yuki Wong Yee Kee
Student No. 10782321
PPS
Final temperature = 52.5 ℃
∆H = m c ∆T
n=CV
= 1 x 25 x 10-3
= (25)(4.18)(52.5-18.7)
= 0.025 mol
= 3532.1 J
= 3.5321 kJ
3.5321 kJ of heat is produced from 0.025 mol of Cu2+
3.5321
1
 141.28 kJmol -1
0.025
⸫ The enthalpy change for one mole of CuSO4(aq) is -141.28 kJmol-1
Evaluation and conclusions
From the result, the enthalpy change for one mole of CuSO4(aq) is -141.28
kJmol-1 which show that the reaction between copper (II) sulphate and zinc is
an exothermic reaction. However, the accepted value for this reaction is -217
kJmol-1 where we have a percentage error of 34.89% .
error 

experiment al value  accepted value
100%
accepted value
 141.28  (217)
100%
 217
 34.89%
To obtain a more accurate result, we can use calorimeter that used for industry
and research typically have a well-insulated, fully enclosed reaction vessel,
motorized stirring mechanism, and a more accurate temperature sensor.
Yuki Wong Yee Kee
Student No. 10782321
PPS
Reference List
Donald, F. et al. (2013) Chemistry Concepts - Intermediate. Available at:
https://www.ck12.org/book/ck-12-chemistry-concepts-intermediate/section/23.
1/ (Accessed: 14 March 2020).
Flowers, P., Theopold, K., Langley, R., and Robinson, W. R. (2018) Chemistry:
OpenStax. Available at:
https://opentextbc.ca/chemistry/chapter/5-2-calorimetry/
(Accessed: 14 March 2020).
Saunders, N. (2003) Determining the enthalpy change of a reaction. Available
at: https://www.creative-chemistry.org.uk/documents/N-ch2-11.pdf
(Accessed: 14 March 2020).
Chemistry Dictionary (2017) Available at:
https://chemdictionary.org/enthalpy-change/ (Accessed: 16 March 2020).
Chung, Y. (2016) Reactivity Series and Redox Reactions. Available at:
https://prezi.com/nk-md1ms6ngu/reactivity-series-and-redox-reactions/
(Accessed: 17 March 2020).
Yuki Wong Yee Kee
Student No. 10782321
PPS