Enthalpy Change Calculator

Enthalpy change is the heat a chemical reaction gives out or takes in at constant pressure, one of the central quantities in chemistry, and this calculator works it out from a calorimetry experiment, the standard way it is measured in the lab and the classroom. Enter the mass of the solution being heated or cooled, its specific heat capacity, the temperature change you measured, and the number of moles of the limiting reactant, and it returns the heat exchanged and the enthalpy change per mole, with the correct sign, updating as you type. The method rests on two simple steps. First, the heat is found from the familiar relationship that heat equals mass times specific heat capacity times the temperature change, which tells you how much energy moved in or out of the solution. Second, that heat is divided by the moles reacting to put it on a per-mole basis, and the sign is flipped, because a temperature rise means the reaction released energy into its surroundings and so has a negative, exothermic enthalpy change, while a temperature drop means it absorbed energy and is endothermic with a positive value. The calculator flags which case you are in, so the meaning is never in doubt. The specific heat defaults to that of water, the most common situation in school experiments where a reaction happens in aqueous solution, but you can change it for other solvents. That makes the tool genuinely useful for chemistry students carrying out and writing up calorimetry practicals, for checking homework on exothermic and endothermic reactions and Hess's law problems, and for anyone needing a quick, correctly signed reaction enthalpy. Using grams, joules per gram per degree, degrees and moles gives an answer in kilojoules per mole. The formula and a worked example are explained clearly below.

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A temperature rise is taken as exothermic (negative enthalpy). Enter the temperature change as positive for a rise.