Question

Which of the following is a chemical change?
A. breaking of a brick
B. evaporation of a liquid
C. burning of a candle
D. moving of a wheel

Answer 1

Hint: A chemical change is a result of any kind of reaction that produces a change in the substances that react together to form products. Any change in the chemical composition of the substance that molds it to bring about a noticeable change can be termed as a chemical change.

Complete answer:
A chemical change is any process that changes the chemical composition of any substance. The chemical composition of the substance is changed such that some by – products are formed. These are a result of species reacting and forming a new product. Physical changes are a result of external force acting that does not change the chemical composition, but only changes the physical form of the substance.
Among the options given, only burning of a candle is a chemical change. As we know the burning is a form of combustion that requires oxygen to carry out the burning process. The candle consists of a wax and a wick which is made up of hydrocarbons. Hydrocarbons when burned produce carbon dioxide, carbon soot, vapors, heat, and light. As the equation of combustion of hydrocarbons suggest as,
$C{H}_4+2O_2\to C{O}_2+2H_{2}O$ . This clearly shows a chemical change.

Hence, burning of candle is a chemical change, so option C is correct.

Note:
Breaking a brick, evaporation of liquid, and moving a wheel, are examples of physical changes as no change is observed in the chemical composition in carrying out these processes. Only the physical appearances of these substances are being changed in the processes.