Heat of Reaction

What is this formula?

The heat of reaction is the enthalpy change associated with a chemical reaction. It represents the amount of heat released or absorbed when reactants are converted into products at specified conditions.

When to use it

Use this equation when performing energy balances, reactor design calculations, combustion analysis, and thermodynamic evaluations of chemical processes.

Example

A reaction produces products with a total enthalpy of -850 kJ/mol, while the reactants have a total enthalpy of -500 kJ/mol.

Formula:

ΔHr = Hp - Hr

Substitution:

ΔHr = -850 - (-500)

Result:

ΔHr = -350 kJ/mol

The reaction releases 350 kJ/mol and is therefore exothermic.

Applications

- Chemical reactor design

- Combustion calculations

- Process energy balances

- Thermodynamic analysis

- Process simulation software

Note

This equation is an exact thermodynamic definition. In practice, the enthalpies used may be obtained from standard formation enthalpies, calorimetric measurements, or thermodynamic property databases. The numerical result depends on the chosen reference state and operating conditions.