During a power cut, Vihaan's mother lit a candle. Vihaan observed that :

• The solid wax near the flame melted and later resolidified, when it dripped onto the table.
• The molten wax at the wick burnt with a flame, producing light, smoke and heat.

Answer the following questions :

(a) Classify the changes below as physical or chemical with justification :

(i) Solid wax melting and resolidifying.

(ii) Molten wax at the wick burning to produce light, heat and smoke.

(b) Name the gases produced when molten wax is burnt.

(c) Burning of wax is an exothermic reaction releasing energy in the form of heat and light. Can you think of an exothermic reaction occurring in living beings?

(a) The changes below are :

(i) Solid wax melting and resolidifying is a physical change because no new substance is formed. Only the state of wax changes, and the change is reversible.

(ii) Molten wax at the wick burning to produce light, heat and smoke is a chemical change because new substances such as carbon dioxide and water vapour are formed, and energy is released in the form of heat and light.

(b) The gases produced when molten wax is burnt are carbon dioxide and water vapour.

(c) Respiration is an exothermic reaction occurring in living beings. During respiration, glucose reacts with oxygen to form carbon dioxide and water, releasing energy in the form of heat.