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Enthalpy of Reaction Calculator

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The Enthalpy of Reaction Calculator is a user-friendly tool designed to simplify the process of calculating the enthalpy change (ΔΔHreaction​) for chemical reactions. This calculator uses the fundamental principles of Hess’s law, which states that the total enthalpy change for a reaction is the sum of all changes over the individual steps of the reaction, making it a crucial tool for students, educators, and professionals in the field of chemistry.

Purpose and Functionality

The main purpose of the Enthalpy of Reaction Calculator is to provide a quick and accurate means of calculating the energy change during chemical reactions, specifically the enthalpy change. Enthalpy change is a measure of the heat absorbed or released during a chemical reaction at constant pressure. This calculator simplifies the calculation by using the formula:


Where ΔΔHreaction​ represents the enthalpy of reaction, ΔΔHproducts​ is the enthalpy of formation for the products, and ΔΔHreactants​ is the enthalpy of formation for the reactants.

Step-by-Step Example

Let’s go through a simple example to illustrate how the calculator works:


  • The enthalpy of formation of 2()H2​O(l) is −285.8−285.8 kJ/mol.
  • The enthalpy of formation of 2()O2​(g) is 00 kJ/mol (since it’s an elemental form).
  • We want to calculate the ΔΔH for the reaction: 22+2→222H2​(g)+O2​(g)→2H2​O(l).


  1. Input the enthalpy of formation for the reactants and products into their respective fields.
    • For 2H2​O(l), input −285.8−285.8 kJ/mol.
    • For 2O2​(g), input 00 kJ/mol.
  2. Input the stoichiometric coefficients of the reactants and products.
    • For 2H2​O(l), input 22.
    • For 2O2​(g), input 11.
  3. Click the “Calculate” button to get the result.

Output: The calculator will display the ΔΔHreaction​ value, which, in this case, would be −571.6−571.6 kJ/mol, indicating the amount of energy released during the reaction.

Relevant Information Table

CompoundEnthalpy of Formation (kJ/mol)


The Enthalpy of Reaction Calculator stands out as an indispensable tool for those studying or working in chemistry. It not only aids in understanding the concept of enthalpy changes in reactions but also enhances efficiency in calculating these values, which are fundamental to the study of thermodynamics and energy exchanges in chemical processes. Its straightforward interface and accurate calculations make it a valuable resource for educational and professional applications alike, enabling users to better analyze and predict the outcomes of chemical reactions.

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