Hess's Law
| Formula / Notation | ΔH_total = ΔH1 + ΔH2 + ΔH3 + ... |
|---|---|
| Also Known As | Hess law of constant heat summation |
What is Hess's Law?
The law stating that the total enthalpy change for a reaction is the same regardless of the pathway taken, as long as initial and final states are the same. This allows calculation of enthalpy changes for reactions that cannot be measured directly by combining known thermochemical equations.
Formula & Notation
Other Names / Synonyms: Hess law of constant heat summation
Properties & Characteristics
Uses & Applications
Safety Information
Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.
Key Facts
Frequently Asked Questions
The law stating that the total enthalpy change for a reaction is the same regardless of the pathway taken, as long as initial and final states are the same. This allows calculation of enthalpy changes for reactions that cannot be measured directly by combining known thermochemical equations.
Calculating ΔH for reactions that are difficult to measure directly. Determining bond energies. Constructing Born-Haber cycles for ionic compounds. Calculating lattice energies of ionic crystals. Thermodynamic analysis of multi-step industrial processes. Fuel energy content estimation.
Theoretical calculation tool. The safety implication is that total enthalpy change is path-independent — useful for predicting heat release in multi-step synthesis routes.
The formula or notation for Hess's Law is: ΔH_total = ΔH1 + ΔH2 + ΔH3 + ...