Question

Fill in the blanks by selecting correct word/term given in the bracket.

Formation of a new substance or new substances is called ___ change. (physical/ chemical)

Answer 1

Physical and chemical changes:

The temporary changes occurring in a substance that does not cause any change in the identity of the substance are called physical changes. These changes are usually reversible and do not change the chemical composition of the substance. Changes occurring in a substance during cooling or heating are examples of physical changes.

Chemical changes are permanent changes occurring in a substance that causes a change in its identity. These changes are generally irreversible and cause a change in the chemical composition of the substance. These changes involve the absorption or evolution of energy.

Properties of a chemical change:

When a new substance is formed, the chemical identity and chemical composition of the substance gets changed. Therefore, the formation of new substances occurs during chemical changes.

For example, the formation of water $\left({\mathrm{H}}_2\mathrm{O}\right)$ from hydrogen $\left({\mathrm{H}}_2\right)$ and oxygen $\left({\mathrm{O}}_2\right)$ is an example of a chemical change in which a new substance, water, is formed from different substances.

$$\begin{gathered} 2{\mathrm{H}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \left(\mathrm{Hydrogen}\right)\left(\mathrm{Oxygen}\right)\left(\mathrm{Water}\right) \end{gathered}$$

Therefore, the formation of a new substance or new substance is called a chemical change.