Use the formula ΔH = Hproducts − Hreactants
Measure heat at constant pressure: ΔH = qp
Use calorimetry data to find q from q = mcΔT
For reactions, sum standard enthalpies of formation: ΔH°rxn = ΣΔH°f(products) − ΣΔH°f(reactants)
For bond energies, use: ΔH ≈ Σ(bonds broken) − Σ(bonds formed)
Use Hess’s law to add known enthalpy changes for stepwise reactions
For phase changes, use tabulated enthalpy values such as ΔHfus, ΔHvap, or ΔHsub
Convert units to kJ when needed
Keep stoichiometric coefficients consistent with the reaction equation