Reaction Enthalpy Calculator
Compute the standard enthalpy change of a chemical reaction from the sum of product and reactant formation enthalpies, with per-mole conversion.
How to Use the Reaction Enthalpy Calculator
- Sum the standard formation enthalpies of all products (in kJ) and enter the total.
- Sum the formation enthalpies of all reactants.
- Enter the number of moles you want to normalise to.
- Click Calculate.
Casos de Uso
- •Hess's law problem sets.
- •Thermochemistry homework.
- •Rapid combustion energy screening.
Fórmula
ΔH°_rxn = Σ ΔH°_f(products) − Σ ΔH°_f(reactants). Negative ΔH indicates an exothermic reaction.
Preguntas Frecuentes
What about non-standard conditions?
Standard enthalpies of formation are at 298.15 K and 1 bar. For other temperatures, add ∫ΔCp dT using Kirchhoff's law.
Where do I get ΔH°_f values?
NIST WebBook, CRC Handbook, or textbook appendices. Always keep consistent reference states (usually gas-phase elements).
Negative means what?
A negative ΔH means heat is released — the reaction is exothermic. Positive means endothermic.