Analyze enthalpy changes from coefficients and formation values. See totals, trends, units, and downloadable reports. Built for quick checks, teaching, labs, and design work.
This sample shows methane combustion using standard enthalpies of formation.
| Side | Species | Coefficient | ΔH°f (kJ/mol) | Contribution (kJ/mol) |
|---|---|---|---|---|
| Reactant | CH4(g) | 1 | -74.8 | -74.8 |
| Reactant | O2(g) | 2 | 0.0 | 0.0 |
| Product | CO2(g) | 1 | -393.5 | -393.5 |
| Product | H2O(l) | 2 | -285.8 | -571.6 |
| ΔH°rxn = Products - Reactants | -890.3 kJ/mol | |||
Standard reaction enthalpy from formation values:
ΔH°rxn = Σ nΔH°f,products - Σ nΔH°f,reactants
Multiply each species standard enthalpy of formation by its stoichiometric coefficient. Add all product contributions. Add all reactant contributions. Subtract reactants from products.
Where:
Negative results indicate heat release. Positive results indicate heat absorption. Standard-state values are commonly referenced at 298.15 K and 1 bar.
It calculates the standard enthalpy change for a balanced chemical reaction using standard enthalpies of formation for reactants and products.
Stoichiometric coefficients control each species contribution. An unbalanced equation gives the wrong product and reactant totals, so the final enthalpy value becomes unreliable.
A negative standard enthalpy change means the reaction is exothermic. The system releases heat to the surroundings under standard conditions.
A positive value means the reaction is endothermic. The system absorbs heat from the surroundings under standard conditions.
No. Use one consistent input unit for every formation value. The calculator converts the final answer into your chosen output unit afterward.
Yes, standard elemental forms in their reference states usually have zero standard enthalpy of formation, such as O2(g) and graphite carbon.
The result is per mole of reaction as written. If you change coefficients, you change the reaction basis and the reported enthalpy change.
Use formation enthalpies when reliable tabulated values exist for all species. They usually provide more accurate standard reaction enthalpies than average bond energies.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.