In chemistry, neutralization reactions occur when you combine two extremely reactive substances together for the purpose of rendering them inactive, or neutral. For example, combining an acid and a base together produces water. Neutralization reactions give off energy, which is known as the heat of neutralization. The molar heat of neutralization, then, is the amount of heat each mole of base you add to the acid (or vice versa) causes the reaction to give off, mole being a unit chemists use to represent large numbers of molecules. Once you determine the change in temperature that occurs, the rest is simple.
Weigh your acid on an electronic balance. Place an empty beaker on the balance and hit the Tare button to cancel out the weight of the beaker, then pour your acid into the beaker and place it on the balance. Record the mass of your acid.
Calculate the change in temperature that occurs during the reaction using a calorimeter, a piece of equipment that both measures temperature and holds the reactant. Add your base to the calorimeter and place your acid (in its beaker) below the calorimeter's mouth. Insert the calorimeter's thermometer into the acid and read the initial temperature. Add the amount of base your reaction specifies to your acid, then read your calorimeter to determine the change in temperature.
Calculate the heat of neutralization using the fomula Q = mcΔT, where "Q" is the heat of neutralization, "m" is the mass of your acid, "c" is the specific heat capacity for aqueous solutions, 4.1814 Joules(grams x °C), and "ΔT" is the change in temperature you measured using your calorimeter. For example, if you started with 34.5 grams of hydrochloric acid at 26°C and its temperature increased to 29.1°C when you added sodium hydroxide to it, you would compute the heat of neutralization as follows: Q = mcΔT = 34.5 g x 4.1814 J/(g x °C) x 3.1°C = 447.48 Joules.
Calculate the number of moles of base you added to determine the molar heat of neutralization, expressed using the equation ΔH = Q/n, where "n" is the number of moles. For example, suppose you added 25 mL of 1.0 M NaOH to your HCl to produce a heat of neutralization of 447.78 Joules. Keep in mind that 1.0 M means one mole per liter. Since you added 25 mL (25/1000, or .025 L) of NaOH, determine moles as follows: 1.0 mol/L x .025 L = .025 mol. In this example, your molar heat of neutralization, ΔH, is 447.48 Joules per .025 moles of NaOH added--447.48/.025, or 17,900 Joules per mole.
TL;DR (Too Long; Didn't Read)
If your directions specify as such, you may add an acid to a base rather than adding the base to the acid. If this is the case, you must weigh the base and calculate the number of moles of acid you add to it.
In order to make your molar heat of neutralization a more manageable value, you can convert it to kilojoules--1 kJ=1,000 J--by dividing it by 1,000. For the example above, ΔH expressed using kJ is 17.9 kJ/mol.