The change in which only the physical state of a substance is changed; no new substance is formed, is called a Physical Change.

The change in which a substance or substances are converted into new substance or substances possessing properties which are different from the original ones is called a Chemical Change.

The change in which a substance or substances are converted into new substance or substances possessing properties which are different from the original ones is called a Chemical Equation.

When two or more reactants combine in a reaction to form a single product, it is called a Combination Reaction.

The chemical reaction in which two or more products are formed from a single reactant is called Decomposition Reaction.

The reaction in which a compound is decomposed by heating it to a high temperature, is called Thermal Decomposition.

The reaction in which a compound is decomposed by passing an electric current through its solution or molten mass, is called Electrolytic Decomposition.

The reaction in which the place of the ion of a less reactive element in a compound is taken by another more reactive element by formation of its own ions, is called Displacement Reaction.

The reaction in which the ions in the reactants are exchanged to form a precipitate is called Double Displacement Reaction.

The reaction in which heat is absorbed is called an Endothermic Reaction.

The reaction in which heat is given out is called an Exothermic Reaction.

The substance in whose presence the rate of a chemical reaction changes, without causing any chemical change to it, is called a Catalyst.

The chemical reaction in which, reactants gain oxygen or lose hydrogen is called oxidation.

The chemical reaction in which, reactants gain hydrogen or lose oxygen is called reduction.

The chemical substance, which brings about an oxidation reaction by making oxygen available are called an Oxidant or Oxidizing Agent.

The chemical substance, which brings about reduction, by making hydrogen available, is called as a Reductant or Reducing Agent.

The reaction which involves simultaneous oxidation and reduction is called an oxidation-reduction or Redox Reaction.