Question

what is hess law?

Answer 1

Dear Student!

Hess law is also known as the law of constant heat summation.

It states that the total amount of heat evolved or absorbed in a chemical process is the same whether the process takes place in one or in several steps i.e. the heat of the reaction is free from the path afforded rather it depends only on the initial reactant and final product.

To illustrate Hess's law, we take the thermal equations of following reactions:

Type A:

A+ B -> AB (energy required = ΔH₁ )

AB+ B -> AB₂ (energy required = ΔH₂ )

Type B :

A +2B -->AB₂ (energy required = ΔH₃ = ΔH₁ +ΔH₂ )

Here, from Hess law it is confirmed that, ΔH₃ = ΔH₁ +ΔH₂