Define enthalpy of a reaction. State and explain Hess's Law of constant heat summation.
The amount of heat evolved or absorbed in a chemical reaction when the number of moles of the reactants as represented by the chemical equation have completely reacted, is called the enthalpy of reaction.
Hess's 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.
Path I :
CH4(g)+2Cl2(g)CH2Cl2(g)+2HCl(g)ΔH10=202.3kJPath II :
CH4(g)+Cl2(g)CH3Cl(g)+HCl(g)ΔH20=98.3kJCH3Cl(g)+Cl2(g)CH2Cl2(g)+HCl(g)ΔH30=104.0kJAdding two steps
C...