Question

In which of the following reactions the energy released is not an enthalpy of atomization?

(a) decomposition of a hydrogen molecule into two hydrogen atoms

(b) decomposition of an oxygen molecule into 2 oxygen atoms

(c) formation of a water molecule

(d) decomposition of chlorine molecule

The question was posed to me during an online exam.

This key question is from Thermodynamics topic in chapter Thermodynamics of Chemistry – Class 11

Answer 1

Right answer is (c) formation of a water molecule

To explain: The enthalpy of atomization is an enthalpy change that occurs when one molecule of a molecule breaks into its atoms, but here the of a water molecule formation does not satisfy the definition of the enthalpy of atomization.