Calculating Heat from Solution Calorimetry

Calculating the heat of a reaction from solution calorimetry means treating the reaction's own heat as equal in magnitude and opposite in sign to the heat gained or lost by the surrounding solution, since the reaction and its solution exchange heat only with each other.

Mixing 50.0 mL of 1.00 M HCl with 50.0 mL of 1.00 M NaOH, both starting at 22.0 °C, raises the combined 100.0-g solution to a maximum of 28.9 °C. Treating the solution's specific heat and density as water's own, the solution's heat gain works out to about 2.9 kJ. Because the reaction's heat is equal and opposite to that gain, the reaction's own heat is −2.9 kJ, and the negative sign confirms the neutralization released heat rather than absorbing it.