Question

What is a chemical change and examples?

Answer 1

A chemical reaction or chemical change can be defined as the conversion of one or more substances to new substances or products. Generally, one substance may undergo decomposition to form new products which can be said to be a chemical change.

Complete answer:
Molecules or compounds may react with other compounds to form new substances. The molecules reacted are called reactants. The new substances formed are called products.
Thus, the conversion of reactants into products can be called a chemical reaction or chemical change. The reactants and products can be separated by a single headed arrow.
Some of the examples of chemical changes were:
Rusting of iron: The iron metal reacts with water vapor to form iron (III) oxide and release hydrogen gas. The formation of iron (III) oxide on the iron rod leads to the formation of a red or brown colored layer. The chemical change can be called a chemical change.
Curdling of milk: The conversion of milk into curd can take place by the bacteria called lactic acid bacteria useful for the curdling of milk.
The process like fermentation can also be termed as a chemical change.

Note:
Chemical change involves the change of reactants into products; the physical state of the matter can also be changed. If reactants are solid or liquids may convert into gases. Thus, the state or phase of the reactants may change with the chemical changes.