Question 16
A student carried out a reaction between magnesium ribbon and aqueous trichloroethanoic acid in order to determine the enthalpy change. The equation for the reaction is shown:
Mg(s) + 2H+(aq) ⟶ Mg2+(aq) + H2(g)
The student measured the initial temperature of the trichloroethanoic acid and again every minute for 3 minutes before adding the magnesium ribbon at the fourth minute.
The student continued to measure the temperature every minute for a further 10 minutes.
The graph for these measurements is shown below.
The student used 240 mg of magnesium and 10.0 cm3 of aqueous trichloroethanoic acid (an excess).
Use these data and information determined from the graph above to calculate the enthalpy change, in kJ mol−1, for this reaction.
Show your working.
Give your answer to an appropriate precision.
(The specific heat capacity of water = 4.18 J K−1 g−1)
(Total 7 marks)