Chapter 8, Problem 8.52SP

When a solution containing 8.00 g of NaOH in 50.0 g of water at 25.0 °C is added to a solution of 8.00 g of HCl in 250.0 g of water at 25.0 °C in a calorimeter, the temperature of the solution increases to 33.5 °C. Assuming that the specific heat of the solution is 4.18 J/(g · °C) and that the calorimeter absorbs a negligible amount of heat, calculate ΔH in kilojoules for the reaction

$\text{NaOH}(aq)+\text{HCl}(aq)\stackrel{}{\to }\text{NaCl}(aq)+{\text{H}}_2\text{O}(l)$

When the experiment is repeated using a solution of 10.00 g of HCl in 248.0 g of water, the same temperature increase is observed. Explain.