Chapter 9, Problem 9.85SP

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 HCI 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 .&degC) and that the calorimeter itself absorbs a negligible amount of heat, calculate $\Delta H$ in kilojoules/mol for the reaction
$NaOH\left(aq\right)+HCI\left(aq\right)\to NaCI\left(aq\right)+H_{2}O\left(l\right)$
When the experiment is repeated using a solution of 10.00 g of HCI in 248.0 g of water, the same temperature increase is observed. Explain.