Chemical reactions

Reorganization of Atoms That Form Different Substances

A chemical reaction is a chemical change where matter (a reagent or reagents) becomes a new substance or substances (a product or products).

Some reactions occur only under certain circumstances (eg heat supply, light or electricity). Some reactions are accompanied by external indications (eg color change, gas leakage, heat or light).

What are the important types of chemical reactions?

  • Synthesis Reaction or Direct Combination It is the reaction where two or more substances combine directly to form a new chemical compound.
    General Formula: A + B ---> AB
    Example: Fe + S ---> FeS
    i.e. Iron + Sulfur ---> Iron Sulfide
  • Decomposition Reaction It is the reaction where a chemical compound breaks down (decomposes) into two or more substances. If decomposition requires a heat source, it is called thermal decomposition.
    General Formula: AB ---> A + B
    Example: ZnCO3 ---> ZnO + CO2
    i.e. Zinc Carbonate (+ Heat) ---> Zinc Oxide + Carbon Dioxide
  • Simple Exchange Reaction It is the reaction where one element replaces another in a chemical compound to produce a new compound and the displaced element.
    General Formula: A + BC ---> AC + B
    Example: Fe + CuSO4 ---> FeSO4 + Cu
    i.e., Iron + Copper Sulphate ---> Iron Sulphate + Copper
  • Double Swap Reaction It is the reaction where two chemical compounds exchange their radicals to form two new compounds.
    General Formula: AB + CD ---> AD + CB
    Example: KCl + AgNO3 ---> KNO3 + AgCl
    i.e. Potassium Chloride + Silver Nitrate ---> Potassium Nitrate + Silver Chloride