Notes 1. Chemical Reactions and Equations - Balancing A Chemical Equation | Class 10 Science - Toppers Study

Notes 1. Chemical Reactions and Equations - Balancing A Chemical Equation | Class 10 Science - Toppers Study

Class 10 notes science chapter 1. Chemical Reactions and Equations

1. Balancing a Chemical Equation by hit and trial method.

Here we would learn the method how to balance a chemical reaction.0

The method which we apply e.i hit and trail or inspecting method. Here we take Equation Fe + H₂O → Fe₃O₄ + H₂ as example I:

Steps; 

(i)  Write each formula in box or imagine that each formula is in box. It is so that       you have to mind no changes should be made inside the box. 

(ii)  Count and list the numbers of atom of different element that present in                 unbalanced equation. Like this

Elements              Reactant                               Product

Fe                          1                                              3

O                           1                                              4

H                            2                                              2

First observe that what element has the maximum number of atoms. It may be from reactant and from product. Using this criteria we find that Fe₃O₄  is that compound and element is O that have maximum 4 atoms. 

To equalise the number of atoms of oxygen, we can put the coefficient 4 with H₂O as 4H₂O. Then we get the equation as,

Fe + 4H₂O → Fe₃O₄ + H₂

(iii)  The next maximum number of atoms having Fe. Which can be equalised

        by same process. 

   Putting the coefficient 3 with Fe as 3Fe in reactant side. Now, the equation    will be

3Fe + 4H₂O → Fe₃O₄ + H₂

(iv)  Finally we come to equalise Hydrogen atom of both side. We observe that          4H₂ in reactant and H₂ in product. Total atom of hydrogen in reactant side           is 4 × 2 = 8 and 2 in product. Then, 

Here we cannot put 2 on LHS and 8 on RHS. (8 ÷ 2 ) =4 , the coefficient will be 4 that equalises hydrogen atom on RHS. So finally equation will be.

3Fe + 4H₂O → Fe₃O₄ + 4H₂        (balanced equation) 

Example II. We take,

HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + H₂O

Steps:

(i)  On observing the above chemical equation we see NO₃ has maximum number of atoms/molecules. To equalise it we have on LHS 1 molecule and on RHS 2 molecules. So  

Here Nitrogen and oxygen have been balanced, then Equation will be;

2HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + H₂O

(ii)  Next calcium is already balanced, now we have to balance only hydrogen atoms.

       ​

Product need 2 as coefficient because (4 ÷ 2) = 2 , then equation will be;

2HNO₃ + Ca (OH)₂ → Ca(NO₃)₂ +2H₂O

(iii)  On counting and listing the numbers of atom of different element that present in equation above.

Elements              Reactant                   Product

O                           8                                  8

N                           2                                  2

Ca                         1                                  1

H                            4                                  4

Hence we get a balanced equation

2HNO₃ + Ca (OH)₂ → Ca(NO₃)₂ +2H₂O

I think now you have learnt how to balance a skeletal equation.