Question

Which one of the following processes involves chemical reaction?

• A. Storing of oxygen gas under pressure in a gas cylinder
• B. Liquification of air
• C. Keep petrol in a china dish in the open
• D. Heating copper wire in presence of air at high temperature

Answer 1

The correct option is D

Heating copper wire in presence of air at high temperature

Changes around us can be of two types:

1. Physical changes: The changes in which only physical properties of the substances change.
2. Chemical changes: The changes in which chemical composition of the substances changes which results in the formation of a new substance. These types of changes can be shown in form of a chemical equation.

The explanation for the correct option:

Option D: The heating of copper wire in presence of air at high temperatures leads to the formation of a new substance that is Copper oxide. This can be written as a chemical equation as follows:

$$\begin{gathered} 2\mathrm{Cu}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2\mathrm{CuO}\left(\mathrm{s}\right) \\ \left(\mathrm{Copper}\right)\left(\mathrm{Oxygen}\right)(\mathrm{Copper}\mathrm{oxide}) \end{gathered}$$

The explanation for the incorrect options:

Option A:

1. If high pressure is applied to gas, it changes its state from gas to liquid.
2. The same happens in the case of Oxygen, it will change its state to a liquid state.
3. Changing of state from gas to liquid is a physical change as there is no change in chemical composition.

Option B: Liquification of air is also a change in the state of gas to liquid which is a physical change. Hence, does not involve any chemical reaction.

Option C: If petrol is kept in open, it gets vaporized resulting in a change of state from liquid to gas. Hence this is also a change in the state, which is a physical change.

Hence, option D is the correct answer: Heating copper wire in presence of air at a high temperature.