Hess' law is the fundamental basis behind all thermodynamic data and measurement. It emerges directly from the law of conservation of energy. The simplest statement of the law is:
"The energy change between two different states is independent of the route taken between them".
Essential idea: In chemical transformations energy can neither be created nor destroyed (the first law of thermodynamics).
The enthalpy change for a reaction that is carried out in a series of steps is equal to the sum of the enthalpy changes for the individual steps.
Applications and skills
Application of Hess's Law to calculate enthalpy changes.
Calculation of ΔH reactions using ΔHf° data.
Determination of the enthalpy change of a reaction that is the sum of multiple reactions with known enthalpy changes.
In Chapter 4.3