Question
What is transition? How is Hess’s law helpful in determining the enthalpy of transition?
Solution
Transition means the conversion of one allotropic form of a substance to another. Hess’s law is very useful in determining the enthalpy changes of those reactions which take place extremely slowly. For example, the transformation of rhombic sulphur to monoclinic sulphur is a very slow process. No direct method is available to determine its enthalpy change. It is calculated by Hess’s law. We aim at the equation,
Experimentally it has been found that
Subtracting equation (ii) from (i), we have,
Experimentally it has been found that
Subtracting equation (ii) from (i), we have,
