Question

What will you take into account while identifying the following?
A chemical change in a substance.

Answer 1

Chemical reactions are the formation of new products. There are two types of changes in chemical reactions. They are physical changes and chemical changes. A chemical change means there is a change mainly in the chemical composition of reactants and products.

Complete answer:
Chemical changes are the changes that are involved in the composition change. Thus, when one substance is taken and treated with another, the substance undergoes a chemical change. This can be known by the formation of new substances.
While identifying the chemical change one must identify the following factors:
Chemical composition will change when a substance undergoes chemical change. For example, calcium carbonate undergoes a chemical change to form calcium oxide. Here there is a difference in composition of atoms in the substance.
Energy will also be changed when a substance undergoes chemical change.
New substances will be formed when a substance undergoes chemical change. The treatment of sodium metal with water forms sodium hydroxide.
The chemical change is not a reversible process all the time. Some compounds can be easily reversible and some cannot be easily reversible.
Liberation of gases like hydrogen gas, carbon dioxide gas is also an identification for a chemical change process.

Note:
While mixing two or more substances, one must be careful in both the physical and chemical changes. As sometimes physical change like color can also give about the completion of a reaction. Physical changes were useful in analysis and chemical changes were useful in synthesis.