When moist suger is treated with anhydrus `CaCl_2`, it removes the moisture from the moist sugar due to its deliquuesent nature. The chemical composition of suger does not change in this process. Hence it is a physical change. When sugar reacts with concentrated `H_2SO_4`, it is converted to black residue called sugar charcoal. Concentrated `H_2DO_4` due to its dehydrating nature removes the hydrogen and oxygen present in the compound as water and the chemical composition of sugar changes. Hence it is a chemical change.
