Question

Which of the following can be reversed?
(A) Melting of wax
(B) Burning of candle
(C) Reduction of size of candle during burning
(D) Solidification of melted wax

Answer 1

Hint: All physical processes are reversible whereas chemical reactions are irreversible.

Complete step by step answer: A reversible change is a physical change that can be undone.
A final substance can be converted back to the original substance without creating any new material.
An irreversible change is a permanent change that cannot be undone.
Melting of wax is a reversible process. Since upon cooling, it changes back to solid wax. Similarly, Solidification of melted wax can be reversed which is the melting of wax. Thus, option A and D are reversible processes.
In case of burning a candle, carbon dioxide, water vapour and soot all go into the air thereby we cannot get back the original candle. Thus, it is an irreversible process. Similarly, Reduction of size of candle during burning cannot also be reversed. A chemical reaction takes place between wax and oxygen. A chemical energy in the form of heat and light is released. A chemical process can never be reversed.

So, the correct options are B and D.

Note: The reversible process will make us get back to the original form whereas in an irreversible process it is not possible. Common reversible processes are:
1. Freezing of ice-cream is a reversible change as it can be reversed back by heating and it will convert to original form.
2. Opening of a door is a reversible change as it can be reversed simply by closing the door.
3. Melting of chocolate is a reversible change as it can be reversed by cooling the chocolate to its original form.