Hess's Law of Constant Heat Summation states that regardless of the multiple stages or steps of a reaction, the total enthalpy change for the reaction is the sum of all changes. This law is a manifestation that enthalpy is a state function.
Germain Henri Hess (1802 - 1850) is important primarily for his thermochemical studies. Hess' Law states that the heat evolved or absorbed in a chemical process is the same whether the process takes place in one or in several steps. This is also known as the law of constant heat summation.
Hi, Raja, it is a very simple law for finding the total enthalpy change of a reaction. According to Hess law, if a chemical reaction consists of multiple steps then by simply adding the enthalpy of each step gives you the total enthalpy change of that reaction. And the reason behind this is Enthalpy is a state function, therefore, it is independent of the path followed to achieve the chemical reaction.
Hess's Law of Constant Heat Summation (or just Hess's Law) states that regardless of the multiple stages or steps of a reaction, the total enthalpy change for the reaction is the sum of all changes. This law is a manifestation that enthalpy is a state function.
This video is power full for details about Hess's Law
https://www.khanacademy.org/science/chemistry/thermodynamics-chemistry/enthalpy-chemistry-sal/v/hess-s-law-example
Also their is discussions below this video for more support
If Hess's Law were not true, then once could easily violate the First Law of Thermodynamics (energy conservation). If the enthalpy change for a given process was, say, larger if carried out in one step than in several steps, then if the process was carried out forward in one step and then backward in several steps, net creation of energy would be realized. Thus Hess's Law can be viewed as a special case of the First Law of Thermodynamics (energy conservation).
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