3.1.4.3 - Hess's law

Hess’s Law

Total enthalpy change of reaction is independent of the route taken

Hess’s Law example

Calculating enthalpy change using enthalpy of formation

• Need to know Δ_fH^⦵ of all reactants + products that are compounds

Hess’s Law equation

Δ_rH^⦵ = sum of Δ_fH^⦵ products - sum of Δ_fH^⦵ reactants

Calculating enthalpy change using enthalpy of combustion

Hess’s Law diagram with backwards arrow example