6.6 Introduction to Enthalpy of Reaction

ΔH°rxn is tied to the balanced equation as written. Double the equation → double ΔH. Reverse it → flip the sign.

Use ΔH as a conversion factor: kJ per mole of reaction.

2H₂ + O₂ → 2H₂O, ΔH = −572 kJ → per mole H₂O = −286 kJ.

Worked example: Heat from 4 mol H₂ → 2 × (−572) = −1144 kJ.