Why decomposition of sugar on heating is an irreversible change.

The heat of formation of the products of the heating of sugar, which is caramel is higher and due to the new complexes formed such there is increased change in free energy between the products and the reactants of the sucrose decomposition by heating, making the reaction is irreversible

Explanation:

Sugar, also known as sucrose, C₁₂H₂₂O₁₁, is a disaccharide made up two monosaccharides, fructose, C₆H₁₂O₆, and glucose, C₆H₁₂O₆ joined together by a glycosidic covalent bond as such the molecule of sugar has one less molecule of H₂O than the fructose and the glucose it is made of which on heating the sugar the glycosidic bonds break and due to deficiency in the amount of H₂O the fructose and glucose combine with themselves to form caramel which has a much lower hydrogen and oxygen proportion such as C₂₄H₂₆O₁₃, which is darker and contains free radicals making caramel sticky.

Therefore, the heat of formation of the caramel is higher and due to the formation of the complexes there is increased change in free energy between the products than the reactants of the decomposition of sugar by heating, therefore, the reaction is irreversible.