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Energy Cycles in Reactions · Paper 2 — Free Chemistry SL Practice Questions

1MasterySAQ-SThermochemistry and enthalpy diagrams5 marksPaper 2~8 min

A student investigates the exothermic reaction between zinc powder and aqueous copper(II) sulfate:

\text{Zn}(s) + \text{CuSO}_4(aq) \rightarrow \text{ZnSO}_4(aq) + \text{Cu}(s)

The student adds

0.0500\,\text{mol}

of zinc powder to

50.0\,\text{cm}^3

1.00\,\text{mol}\,\text{dm}^{-3}

aqueous copper(II) sulfate in a polystyrene cup. The initial temperature of both reactants is

21.5\,°\text{C}

. After stirring, the maximum temperature reached is

38.2\,°\text{C}

. Assume the specific heat capacity of the solution is

4.18\,\text{J}\,\text{g}^{-1}\,\text{K}^{-1}

and the density of the solution is

1.00\,\text{g}\,\text{cm}^{-3}

(a)

State which species — reactants or products — has the higher enthalpy in this reaction. [1 mark]

(b)

Calculate the enthalpy change,

\Delta H

, for this reaction in

\text{kJ}\,\text{mol}^{-1}

of zinc reacted. Give your answer to three significant figures. [2 marks]

(c)

The accepted standard enthalpy change for this reaction is

-216\,\text{kJ}\,\text{mol}^{-1}

. Explain two reasons why the student's experimental value differs from this accepted value. [2 marks]

Solutions

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