🔥Enthalpy Calculator
Enter each species' coefficient and standard formation enthalpy to find ΔH of reaction via Hess's law.
Default: CH₄ + 2O₂ → CO₂ + 2H₂O. One species per line: "coefficient, ΔHf° (kJ/mol)". Elements in their standard state have ΔHf° = 0.
Free Enthalpy Calculator
This enthalpy calculator applies Hess's law to find the overall enthalpy change of a reaction: ΔH°rxn = Σ(n × ΔHf° products) − Σ(n × ΔHf° reactants). Enter each species' stoichiometric coefficient and standard enthalpy of formation, and the calculator sums both sides and subtracts.
Hess's law states that the total enthalpy change for a reaction is the same regardless of the path taken — it only depends on the initial and final states. This makes it possible to calculate ΔH for reactions that are difficult to measure directly, using tabulated formation enthalpies.
A negative ΔH means the reaction is exothermic (releases heat); a positive ΔH means it's endothermic (absorbs heat). Free, runs entirely in your browser.