Hess's law and thermochemical accounting
Reaction enthalpies can be combined because enthalpy is a state function.
Key knowledge
Hess's law states that reaction enthalpy changes add when the corresponding balanced reactions add. Reversing a reaction reverses its enthalpy change; scaling its stoichiometry scales the change. The result depends on initial and final states rather than the chosen path.
Conditions and scope
- Use compatible temperatures, pressures, phases and stoichiometric reference amounts.
- Measured heat equals enthalpy change under the appropriate constant-pressure, pressure–volume-work conditions.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Source state-function reasoning and thermochemical examples, not a new calorimetric measurement.
2026-10-10 · Checked additive bookkeeping and heat/enthalpy boundary.
Entry details
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- chem-hess-law
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