*              Chemical reaction:-

                The reaction which occurs during the chemical change is called chemical reaction.

*              Chemical equation:-

                The symbolic representation of the chemical reaction in terms of symbols and formula is called chemical equation.

*              The conditions: Required for the chemical reaction are:

                i)             Simple contact:- NH3+HCL®NH4CL

                ii)            Solution: AgNO3+NaCL® AgcL+NaNO3

                iii)           Pressure: N2+3H2®2NH3

                iv)           Heat: CaCo3®CaO+CO2

                v)            Light: 6CO2+6H2O ®C6H12O6+6O2

                vi)           Electricity: 2H2O ® 2H2+O2

                vii)          Catalyst: 2H2O2(MnO2) ®2H2O2+O2

*              Main types of chemical reaction are:-

                a)             Combination reaction

                                2Na+Cl2 ®2NaCl

                        b)            Decomposition reaction:-


                c)             Displacement reaction (single and Double)

                                Zn+H2SO4 ® ZnSO4 + H2

                d)            Acid-base reaction:-

                                HCl+ NaOH®Nacl+H2O

Molecular weight:-

                The sum of the atomic weights of all the atoms of same or different elements present in a molecule is called molecular weight.

                1.             amu=1.67×10-24 grm.

Gram molecular weight:-

                The molecular weight of a substance expressed in terms of grams is called gram molecular weight.

                Avogadro’s Number:-

                The number of atoms, moleculer or ions in one mole of any substance is called Avogadro’s Number.

                Avogadro’s No.=6.023×1023

                The collection of 6.023×1023 number of particles of atoms or molecules or ions is known as mole.

*              Information conveyed by balanced chemical equations:

                i.              The names of the reactants and products.

                ii.            The number of atoms or molecules of reactants and products. 

                iii.           The types of chemical reaction.

                iv.           The ratio of weight of molecules of reactants and products.

*              Limitation of chemical reactions:

                i.              How long does the reaction take to complete.

                ii.            The concentration of reactants.

                iii.           Whether the reaction occurs faster or slower.              

                iv.           Whether the reaction occurs by itself or it require certain conditions.

*              Rate of chemical reaction;

                The change in concentration of the reactant or product per unit time is called the rate of chemical reaction.

Rate of chemical reaction is directly proportional to  Concentration

                Rate of chemical reaction is inversely proportional to  Surface area of reactants


1.     Acid-base reaction is called neutralization reaction.

        Ans- During the chemical reaction, both acid and base lose their properties so as to form neutral substance (i.e. salt and water). Hence, acid-base reaction is called neutralization reaction.

2.     Chemical equation is balanced


        It is necessary to obtain a balanced chemical equation.

        Ans-According to the law of chemistry, the mass of reactants is equal to the mass of products. The mass of each elements appearing in the reaction is conserved for which the no. of atoms of each elements on the reactant side must be equal to that on the product side. So, chemical equation is balanced.