Energetics

Enthalpy change ($\Delta H$) is the heat energy change at constant pressure. Exothermic reactions release heat ($\Delta H$ negative); endothermic absorb it ($\Delta H$ positive).

Calorimetry

Measure heat using: $$q = mc\Delta T$$ where $m$ = mass of solution (g), $c$ = specific heat capacity (4.18 J g⁻¹ K⁻¹), $\Delta T$ = temperature change. Then $\Delta H = -\dfrac{q}{n}$ (in kJ mol⁻¹; negative if temperature rose).