Some of the most important facts of Chemical Reactions are :
1. Breaking or rearrangement of bonds between atoms or groups of atoms results in chemical reactions.
2. Chemical reactions can be classified on the basis of
a. Physical state of the reactants and products,
b. Direction of the reaction,
c. Absorption or evolution of heat during the reaction, and
d. The nature of the chemical reaction.
3. In homogeneous reactions, reactants and products are in the same physical state. In heterogeneous reactions, reactants and products are not in the same physical state.
4. In irreversible reactions, the reactants are completely converted into products. The reaction proceeds in the forward direction. In reversible reactions, only a part of the reactants gets converted into products and both the reactants and products remain in equilibrium with each other.
5. Heat energy is given out in exothermic reactions. Endothermic reactions require heat to proceed.
6. In synthesis or combination reactions, two or more reactants combine to form the products.
7. When a substance decomposes to form two or more simpler compounds then such a reaction is called a decomposition reaction.
8. In displacement reactions one part of a molecule is replaced by another.
9. Oxidation can be defined as combination with oxygen or removal of hydrogen or gain of electrons by an ion, atom or molecule.
10. Reduction can be defined as the loss of oxygen or combination with hydrogen or gain of electrons by an ion, atom or molecule.
11. Both oxidation and reduction both take place simultaneously.
12. In rearrangement reactions, rearrangement of chemical bonds takes place in such a way that a molecule of one compound is changed into the molecule of another compound.