Hess's law states that :

Options

A. The standard enthalpy of an overall reaction is the sum of the enthalpy changes in individual reactions
B. Enthalpy of formation of a compound is same as enthalpy of decomposition of the compound into constituent elements, but with opposite sign
C. At constant temperature the pressure of a gas is inversely proportional to its volume
D. The mass of a gas dissolved per litre of a solvent is proportional to the pressure of the gas in equilibrium with the solution

Answer

A

Explanation

According to Hess’s law that the total heat change `(Delta H)` accompanying a chemical reaction is the same whether the reaction takes place in one or more steps. It means that heat of a reaction depends only on the initial reactants and final products and not on intermediate products that may be formed.
Now, `DeltaH = DeltaH_1 + DeltaH_2 + Delta H_3`
Enthalpy change in a reaction is always constant and independent of the path followed.