How to Calculate Energy Released & Absorbed

••• valterdias/iStock/GettyImages

Every chemical reaction either absorbs or releases energy. Energy is described in kilojoules per mole, which is a unit of measurement reflecting the amount of energy stored within a material. To determine how your chemical reaction is using energy, you will need to take specific measurements of the reaction itself, then calculate those values using a standard equation. These steps are recommended for those with a basic understanding of working with chemical reactions. Make sure that you are wearing proper safety equipment and that you are familiar with the chemicals being used.

    Research the specific heat capacity value for your first reactant. See the Resource links for lists of the heat capacities of many common substances.

    Fill two separate containers with the reactants. Weigh each container to determine the mass of the reactant. Record these measurements in grams.

    Measure the temperature of the first reactant with a thermometer. Record this measurement.

    Add the second reactant to the first container. Measure the temperature of the combined reactants. Record this value.

    Insert the measurements taken from the previous steps into the following equation:

    Energy = (mass of first reactant + mass of second reactant) x Specific Heat Capacity x (temperature of first reactant - temperature of combined reactants)

    This equation will calculate the number of kilojoules per mole released by the first reactant. To determine the energy absorbed, assign a negative value to the equation's solution.

    Things You'll Need

    • Two or more chemical reactants
    • Two or more chemistry containers (flasks, beakers, etc.)
    • Standard lab thermometer
    • Notepad and pen
    • Calculator (recommended)
    • Safety goggles and gloves


About the Author

Marie Cartwright began writing in 2010. Her work has appeared on various websites. Having held office jobs in copywriting and editing, Cartwright now works from her home in Northern California. She also maintains an events website geared toward the science and technology community.