Question

Which of the following is not a physical change?

• A. Boiling of water to give water vapor
• B. Melting of ice to give water
• C. Dissolution of salt in water
• D. Combustion of Liquified Petroleum Gas (LPG)

Answer 1

The correct option is D

Combustion of Liquified Petroleum Gas (LPG)

The explanation for the correct option:

Physical change: The changes in which there is only change in physical property and no new substance is formed.

Chemical change: The changes in which there is a change in chemical composition and a new substance is formed during the process. Generally, these types of reactions are irreversible reactions.

(D) Combustion means burning which means a reaction in which oxygen is involved. Here, the LPG is mostly propane (${\mathrm{C}}_3{\mathrm{H}}_8$) and on burning, it is producing heat energy, water (${\mathrm{H}}_2\mathrm{O}$), and Carbon dioxide$\left({\mathrm{CO}}_2\right)$ as the product. Hence, this process is a chemical change and not a physical change.

$$\begin{gathered} {\mathrm{C}}_3{\mathrm{H}}_8\left(\mathrm{g}\right)+5{\mathrm{O}}_2\left(\mathrm{g}\right)\to 3{\mathrm{CO}}_2\left(\mathrm{g}\right)+4{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \mathrm{Propane}\mathrm{Oxygen}\mathrm{Carbon}\mathrm{dioixde}\mathrm{Water} \end{gathered}$$

The explanation for incorrect options:

A: Boiling of water to give water vapor is a physical change because no new substance is formed. There is a change in the state of water from the liquid state to a gaseous state.

$$\begin{gathered} {\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\stackrel{∆}{\to }{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right) \\ \mathrm{Liquid}\mathrm{water}\mathrm{Water}\mathrm{vapour} \end{gathered}$$

B: Melting of ice to form water is also a physical change as there is only a change in the state of water from solid to liquid.

$$\begin{gathered} {\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)\stackrel{∆}{\to }{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \mathrm{Ice}\mathrm{Liquid}\mathrm{water} \end{gathered}$$

C: Dissolution of salt is also a change in which the state of salt is changing from a solid-state to a liquid state by dissociation of sodium chloride into its ions. Hence, it is a physical change.

$$\begin{gathered} \mathrm{NaCl}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{Na}}^{+}\left(\mathrm{aq}\right)+{\mathrm{Cl}}^{-}\left(\mathrm{aq}\right) \\ \mathrm{Sodium}\mathrm{Water}\mathrm{Sodium}\mathrm{Chloride} \\ \mathrm{Chloride}\mathrm{ions}\mathrm{ions} \end{gathered}$$

Conclusion: Hence, the Correct option is D i.e., Combustion of Liquified Petroleum Gas (LPG).