Hess's Law

📊 intermediate

$$\Delta H_{\text{rxn}} = \sum \Delta H_f(\text{products}) - \sum \Delta H_f(\text{reactants})$$

Total enthalpy change for a reaction is the same regardless of the path taken.

Variables & Units

$\Delta H$

Enthalpy change

Unit: kJ/mol

Key Information

📐 Derived From

Enthalpy as a state function.

💡 Example

Calculating heat of combustion from heat of formation.

🔧 Applications

Calculating reaction heats for unstable reactions.

⚠️ Constraints

Constant pressure.

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