Chemical changes take place when there is a change in the chemical composition of a substance. Physical changes, on the other hand, take place without changes in the material's chemical composition. When we burn a candle, a number of physical and chemical changes take place. The melting of wax is a physical change, since it is still wax and no new bonds have been formed. The burning of wax is a chemical change, since we no longer have the same amount of wax that we started off with. The burning of wick or rope, in the presence of oxygen, releases carbon dioxide gas and also produces soot and represents a chemical change. The molten wax freezes again and represents a physical change.
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