1. The data below are from an experiment to measure the enthalpy change for the reaction of aqueous copper(II) sulfate, CuSO4 (aq) and zinc, Zn (s).

Cu2+(aq) + Zn(s)→ Cu(s)+ Zn2+(aq)

50.0 cm3 of 1.00 mol dm–3 copper(II) sulfate solution was placed in a polystyrene cup and zinc powder was added after 100 seconds. The temperature-time data was taken from a data-logging software program. The table shows the initial 23 readings.

A straight line has been drawn through some of the data points. The equation for this line is given by the data logging software as


where T is the Temperature at time t.

(a) The heat produced by the reaction can be calculated from the temperature change, DT, using the expression below.

Heat change = Volume of CuSO4 (aq) × Specific heat capacity of HO2×▲T

Describe two assumptions made in using this expression to calculate heat changes.

(b) (i) Use the data presented by the data logging software to deduce the temperature change, ▲T, which would have occurred if the reaction had taken place instantaneously with no heat loss.

(ii) State the assumption made in part (b) (i).

(iii) Calculate the heat, in kJ, produced during the reaction using the expression given in part (a).

(c) The colour of the solution changed from blue to colourless. Deduce the amount, in moles, of zinc which reacted in the polystyrene cup.

(d) Calculate the enthalpy change, in kJ mol–1, for this reaction.

(e) An experiment was designed to investigate how the enthalpy change for a displacement reaction relates to the reactivities of the metals involved. The following metals in order of decreasing reactivity were available.

Excess amounts of each metal were added to 1.00 mol dm–3 copper(II) sulfate solution. The temperature change was measured and the enthalpy change calculated.

(i) Suggest a possible hypothesis for the relationship between the enthalpy change of the reaction and the reactivity of the metal.

(ii) Sketch a graph on the diagram below to illustrate your hypothesis.




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