In a reaction that occurs in 50 g of aqueous solution, the temperature of the reaction mixture increases by 20 °C. If 0.10 mol of the limiting reagent is consumed, what is the enthalpy change (in \({\text{kJ}}\,{\text{mo}}{{\text{l}}^{ - 1}}\)) for the reaction? Assume the specific heat capacity of the solution \( = 4.2{\rm{k}}{{\rm{J}}^{ - 1}}{{\rm{K}}^{ - 1}}\).

A.     \( - 0.10 \times 50 \times 4.2 \times 20\)

B.     \( - 0.10 \times 0.050 \times 4.2 \times 20\)

C.     \(\frac{{ - 50 \times 4{\text{.}}2 \times 20}}{{0{\text{.}}10}}\)

D.     \(\frac{{ - 0{\text{.}}050 \times 4{\text{.}}2 \times 20}}{{0{\text{.}}10}}\)

D

There was a mistake in the units for heat capacity in this question (\({\text{kJ}}\,{\text{k}}{{\text{g}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}\) rather than \({\text{kJ}}\,{{\text{K}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}\)), but this did not appear to put students off as the Difficulty Index and Discrimination Index were both of the order of magnitude that was anticipated.