By Robert Schrader • Updated August 30, 2022
Neutralization reactions—such as the combination of an acid and a base—yield heat known as the heat of neutralization. The molar heat of neutralization quantifies the energy released per mole of reactant added. Determining this value is straightforward once you measure the temperature rise during the reaction.
Place an empty beaker on an electronic balance and press Tare to zero the scale. Add the acid to the beaker, transfer the beaker to the balance, and record the mass. The acid mass is the “m” term in the heat calculation.
Use a calorimeter to record the temperature shift. Submerge the calorimeter’s thermometer in the acid solution, note the initial temperature, then add the base as specified. Read the final temperature and compute ΔT = T_final – T_initial.
Apply the equation Q = m c ΔT, where c = 4.1814 J (g °C)^‑1 for aqueous solutions. For example, with 34.5 g of HCl that warms from 26 °C to 29.1 °C: ΔT = 3.1 °C, so Q = 34.5 g × 4.1814 J (g °C)^‑1 × 3.1 °C = 447.48 J.
Calculate the number of moles of base added. If 25 mL of 1.0 M NaOH is used, n = 1.0 mol L⁻¹ × 0.025 L = 0.025 mol. Then ΔH = Q ÷ n = 447.48 J ÷ 0.025 mol = 17 900 J mol⁻¹ (≈ 17.9 kJ mol⁻¹).
Weigh the acid, record the temperature rise, compute Q with Q = m c ΔT, then divide by the moles of base added to find ΔH. Convert J mol⁻¹ to kJ mol⁻¹ by dividing by 1 000.
