Chemistry / Unit 4 Chem 0663 worked example, 60 to 90 seconds
Calculating Heat from Solution Calorimetry
The idea
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.
In practice
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.
Where people slip
Reporting the solution's own positive heat gain as if it were the reaction's heat, without flipping its sign, mislabels a genuinely exothermic reaction as endothermic.
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