# Determination of an Enthalpy Change of a Reaction

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• Published : April 22, 2011

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Chemistry Internal Assessment 2011
Candy Au

Introduction
The reaction between zinc and copper (II) sulphate is endothermic. If an excess of zinc powder is added to a measured amount of aqueous copper (II) sulphate in a calorimeter and the temperature change is recorded over a period of time, the enthalpy change of the reaction can be experimentally determined. Assumption

1. Mass of H2O in 100cm3 of CuSO4 solution is 100g
2. Specific heat of solution is 4.18 kJ kg-1 K-1 which is the same as the specific heat of water 3. Heat evolved in the reaction will be absorbed by the CuSO4 solution 4. Maximum temperature that would have been reacted if no heat lost to surroundings can be calculated by extrapolation the graph plotted with temperature against time. Procedure

I. Measure 100cm3 of the copper sulphate solution into the II. Weigh about 5 grams of zinc powder.

III. Place the thermometer through the hole in the calorimeter lid then put the thermometer into the copper (II) sulphate solution. Try to keep the solution covered as much as possible from this point on.

IV. Record the temperature of the copper (II) sulphate solution to the nearest 0.1 oC every 60.0 seconds for 25 minutes.

V. At precisely 3.0 minutes, add zinc powder to the cup. Swirl the mixture gently.

VI. Continue to swirl the contents of the calorimeter and record the temperature for an additional 6 minutes.

VII. Dispose of the products of this reaction in the waste container.

Zn(s) + CuSO4(aq) Cu(s) + ZnSO4(aq)

Amount of CuSO4 = 1001000 ×1=0.1 mol
Amount of Zn = 565.37=0.07649 mol
Therefore Zn is the limiting reagent

ΔT=56.75-25=31.75 or 31.75 (K)
Mass of H2O = 100cc×1g per cc
Heat evolved = 1001000 ×4.18 ×31.75=13.2715 kJ
Therefore enthalpy change for the reaction

ΔH= -13.2715 × 10.07649
ΔH= -173.51 kJ mol-1
ΔH reaction literture= -210.16 kJ mol-1

% difference from literature= 210.16-173.51210.16 ×100%
% difference...