Enthalpy Changes On Displacement And The Reactivity Series
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This experiment will test the suggestion that the enthalpy change between a metal and a solution of a salt is related to the relative position of the two metals in the reactivity. Presumably the further apart in the series the bigger the enthalpy change will be.
The experiment is as follows,
1) Zn(s) + CuSO4(aq) ZnSO4(aq) + Cu(s)
2) Zn(s) + Pb(NO3)2(aq) Zn(NO3)2 (aq) + Pb(s)
Both of the solutions will be in 1mol.dm-3
Apparatus:
Distilled Water
Polystyrene Cup
Polystyrene Lid for cup
Thermometer
1mol.dm-3 Copper Sulphate Solution
1mol.dm-3 Lead Nitrate Solution
Zinc
25cm3 Measuring Cylinder
Safety Goggles
Balance
Readings
For this experiment the readings that you will need to take are the starting temperature of the solution being used and the maximum temperature that the solution reaches after zinc has been added.
I have decided to use 25cm3 of each solution for the experiment this is 0.025mols of each therefore we need 0.025mols of zinc to react with it,
1 mol of Zn = 65g
65 x 0.025mols = 1.625g
This means that 1.625g of zinc will be required in this reaction however we will use 1.8g to ensure the zinc is in a reasonable excess. This will not affect the results because only as much as needed will be used.
Method
Clean out the equipment with distilled water to ensure there is no contamination.
Prepare 25cm3 of copper sulphate solution in a polystyrene cup.
Prepare 1.8g of zinc in a weighing boat.
Measure and record the starting temperature of the solution
Add the zinc to the solution and simultaneously place the lid over the cup and thermometer
Gently stir the solution with the thermometer to ensure an even temperature throughout the solution.
Observe the thermometer and record the maximum temperature that the solution reaches.
Record the results and use them to calculate the energy change.
Repeat these steps for the lead nitrate solution.
Calculating Enthalpy Change
From the results we get from this we can then go on to calculate the enthalpy change in kJ.mol-1 as follows
Firstly for example if we had a starting temperature of 25oC and the maximum temperature that the solution reached was 30oC.