Hess's law states that the total enthalpy change during a chemical reaction is the same regardless of the path or number of steps taken to complete the reaction. In other words, the change in enthalpy depends only on the initial and final states of the reactants and products, not on the specific process or route taken. This principle is based on enthalpy being a state function and is a consequence of the first law of thermodynamics. Hess's law allows calculation of enthalpy changes for reactions that occur in multiple steps by summing the enthalpy changes of each step.
Key points about Hess's law:
- Enthalpy change (ΔH) is independent of the reaction pathway.
- It applies to reactions at constant pressure.
- It enables determination of enthalpy changes that are difficult to measure directly.
- It is foundational in thermochemistry for calculating heat transfer during reactions.
This makes Hess's law a fundamental tool for understanding and calculating energy changes in chemical processes.
