KIST
Determining Enthalpy Change
Research Question
How can you determine the enthalpy change for a displacement reaction?
Scientific Background
The reaction to be investigated is that between zinc and less reactive copper. By
adding an excess of zinc powder to a measured amount of aqueous copper (II)
sulphate, and measuring the temperature change over a period of time you can then
calculate the enthalpy change for the reaction.
Variables
N/A
Chemicals needed
Chemical
Zinc powder
Hazard
Precaution
Disposal
0.5M Copper (II)
sulphate solution
Apparatus needed
Safety spectacles
Pipette, 25 cm3
Pipette filler
Polystyrene cup
Weighing bottle
Spatual
Electronic balance
Temperature probe
Stop watch
Diagram
N/A
Method
1. Pipette 25.0 cm3 of the copper (II) sulphate solution into a polystyrene cup.
2. Weigh about 1 g of zinc powder in the weighing bottle. There is no need to
be accurate.
3. Put the temperature probe through the hole in the lid, stir and record the
temperature to the nearest 0.1 C every 30 seconds for 2 minutes.
4. At precisely 2 minutes, add the zinc powder to the cup.
5. Continue stirring and record the temperature for an additional 7.5 minutes.
6. Repeat steps 1-5 3times.
IB Chemistry Topic 5 Energetics
KIST
Results table
Time/minutes
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
Temperature/C
Data processing
1. Plot the temperature against time.
2. Extrapolate the curve to 3.0 minutes to establish the maxim temperature rise
(T)
3. Calculate the enthalpy change for the quantities used.
4. Calculate the enthalpy change for one mole of Zn and CuSO4(aq), and write
the thermochemical equation for the reaction.
Uncertainty Calculation
Compare you result with the accepted value of -217 kJ mol-1 by calculating the
percentage error in your answer.
Error = experimental value – accepted value x 100
accepted value
Concluding statement and explanation
Evaluation of procedure and results (Formative Assessment)
Problem with procedure
IB Chemistry Topic 5 Energetics
Effect on results
Improvement