Question

iii. State Hess's law of constant heat summation. Illustrate with
an example. State its applications. ​

Answer 1

Hess's law of constant heat summation:

The law states that the change in enthalpy for a reaction is the same whether the reaction takes place in one or a series of steps. The Hess's law can also be stated as the enthalpy change for a chemical reaction is the same regardless of the path by which the reaction occurs.

For example, consider following two paths for the preparation of methylene chloride

1st photo

Thus whether we follow path I or path II, the enthalpy change of the reaction is same.

2nd photo

Answer 2

Answer: According to Hess's law

Explanation: The thermochemical equations can be added, subtracted or multiplied like algebraic equations to obtain the desired equation.