(a) State Hess's Law. Give an example
Answers
Answer:
The Hess's Law States that when reactants are converted to products , the change in enthalpy is the same whether the reaction takes place in one step or in a series of step.
Explanation:
Consider the reaction for the formation of carbon monoxide (CO) from graphite,
C(graphite) + 1/2 (o)2 g ---->> CO (g)
However, burning graphite also produces carbon dioxide (CO)2 , so we cannot measure the enthalpy of change of CO directly.
Instead we employ indirect route, based on Hess's Law. It is possible to carry out the following two reactions which do go to completion,
a). C(graphite) + (O)2 g --->>> (CO)2 g ΔH = -393.5 KJ/mol
b). CO g + 1/2 (o)2 g --->>> (CO)2 g ΔH = -283.0 KJ/mol
Reverse equation (b),
c). (CO)2 g ---->>> CO g + 1/2 (o)2 g ΔH = +283.0 KJ/mol
I hope it helps.
❤.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 .
