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.