Question

Classify the changes involved in the following processes as physical or chemical changes.
(A) Photosynthesis
(B) Dissolving sugar in water
(C) Bumping of coal
(D) Melting of wax
(E) Beating aluminium to from aluminium foil
(F) Digestion of food

Answer 1

Hint: To answer the given question it is important to understand the difference between physical and chemical changes and the fact that Physical changes do not affect the chemical composition of a substance.

Complete step by step solution:
First we should know about physical and chemical changes. Physical changes only affect or change the appearance of a substance. It does not affect the chemical composition of the substance. Whereas chemical changes cause a substance to change into an entirely new substance having a new chemical formula, this is why chemical changes are also known as chemical reactions. Physical changes include bending or dissolving or freezing or boiling etc. the change of states is also a physical change. Chemical changes are also known as chemical reactions and we know that in chemical reactions reactants are transformed into products. The formation of gas bubbles is an example of chemical change, but the formation of gas bubbles during the process of boiling of water is not a chemical change.After reading the above two paragraphs we can say that:
-Photosynthesis is a chemical change because in this process plants convert the light energy into chemical energy. The chemical reaction involved is:
\[6C{{O}_{2}}+6{{H}_{2}}0\xrightarrow{solar energy}{{C}_{6}}{{H}_{12}}{{O}_{6}}+6{{O}_{2}}\]
-Dissolving sugar in water is a physical change because the chemical formula after dissolving sugar in water is the same as the chemical formula at the beginning of the reaction.
-Bumping of coal is a chemical change because coal burning in air produces carbon dioxide and the remaining residue is ash.
-Melting of wax is a physical change because no new substance is formed when only the solid wax is converted to liquid wax and vice versa.
-Beating aluminium to form aluminium foil is a physical change because with beating or molding no new substance is formed.

Note: The change of color and release of odor is a chemical change, as there are many reactions which involve a change in color which happens only when they undergo an oxidation or reduction reaction which is a chemical change.