Key Concepts: Hess's Law

Core Definitions

• Hess's Law: The total enthalpy change for a reaction is the same regardless of the pathway taken.
• Application: Add ΔH values of individual steps to find the overall ΔH of a reaction.
• Reversing a Reaction: Changes the sign of ΔH. If forward is −100 kJ, reverse is +100 kJ.
• Multiplying a Reaction: Multiply ΔH by the same factor. If doubled, ΔH doubles.