Chemical reaction is a PROCESS of forming new product by the reaction of two or more than two reactants. Chemical reactions occurs when two reactants of similar or different properties react together. A new substance is formed when the different chemicals are reacted together.

Examples of chemical reaction:

• Na + Cl  ----> Nacl

• NaOH + H2SO4 -----> Na2SO4 + H20

In a chemical reaction, The two reactants react with each other to form new product. The new product formed may have same physical properties, but the chemical properties always changes. While chemical reaction, no atoms are destroyed nor new atoms are formed. Only, The atoms are rearranged to form new substance.

Chemical reactions are of 4 types: Composition, Decomposition, Single replacement , Double replacement.

Composition

• A + B  →  AB  (One product from two reactants)

Decomposition reaction

• AB  →  A + B  (Two products from one reactant)

Single Displacement reaction

• A + BC    →  AB + C  (One of the element is replaced)

Double displacement reaction

• AB + CD    →  AD + BC (Both of the elements are replaced)

Examples of Chemical reaction:

• CH4 + 2O2 → CO2 + 2H2O

• C4H6O6 + NaHCO3 → NaC4H5O6+ H2O + CO2

• Na + Cl → NaCl

• 2 H2O → 2 H2 + O2

• HBr + NaOH → NaBr + H2O

What does a formula tell about substance:

• Formula of a substance tells us which substance are present in the reaction.

• We know about the proportion of a SPECIFIC chemical used in it.
• Formula of substance tells it's nature, state, position, temperature and it's physical and chemical properties.

• Its chemical formula helps us to get know about the no. of atoms and molecules in it.

Example:

• Let's CONSIDER the example of Hydrochloric acid. We know the formula of Hydrochloric acid - H2SO4

• In this formula, there are elements called Sulphur, oxygen and HYDROGEN. Also, because of formula, we are able to understand it's all components and compounds in it.

• We can also know about it's Molar mass and molecular mass. We can also know about the proportion of the substance in it.