state and explain the Hess law of constant heat summation
Answers
Hᴇss Lᴀᴡ ᴏғ Cᴏɴᴛᴀɴᴛ Hᴇᴀᴛ Sᴜᴍᴍᴀᴛɪᴏɴ
It states that, “The amount of heat evolved or absorbed in a chemical change is the same whether the process takes place in one step or in several steps”.
Applications of Hess’s law: ♠Determination of transition
It helps in the determination of enthalpy of transition during allotropic modification.
♠ Determination of enthalpy of formation
It helps in the determination of enthalpy of formation which cannot be determined experimentally e.g. it is not possible to calculate enthalpy of formation of CO experimentally, but can be calculated by Hess’s law
♠ Bond Energy
It may be defined as, “The quantity of heat evolved when a bond is formed between two free atoms in a gaseous state to form a molecular product in a gaseous state”. It is also known as enthalpy of formation of the bond.
❤.Hess law : "The total heat change in a reaction is the same whether the chemical reaction takes place in a single step or in several steps".
❤.It is based on the I law of thermodynamics .
