Question

Classify the following change as chemical and physical change:

Dissolving common salt in water

Answer 1

Dissolving common salt i.e.; Sodium chloride $\left(\mathrm{NaCl}\right)$ in Water $\left({\mathrm{H}}_2\mathrm{O}\right)$ is a physical change.

• This is because dissolution of salt in water is a physical combination salt in water and no new chemical substance is formed during the process.
• It is temporary and reversible change as salt can be recovered back into its solution.

Chemical change: A change in which one or more new substances are formed and there is a change in the chemical composition of the substance undergoing the change.

• It is a permanent change and irreversible change as the substance undergoing change can not be brought back to its original state.
• Physical as well as chemical properties of the substance change during a chemical change and energy is either consumed when bonds are broken or released when chemical bonds are formed. Examples: Rusting of Iron $\left(\mathrm{Fe}\right)$, Burning of wood.

Physical change: A change in which no new substance is formed and there is no change in the chemical composition of the substance undergoing the change.

• It is a temporary change and reversible change as most of the times, the substance can be brought back to its original state.
• Only physical properties like hardness, colour etc. are changed during a physical change and energy is neither consumed nor released as chemical bonds are not involved in the physical change. Examples: Conversion of Water $\left({\mathrm{H}}_2\mathrm{O}\right)$ from solid to liquid form, melting of wax.