Balancing chemical equations is one to the most important topic in class 9 and 10 Science. In RBSE exams, students often lose marks in this topic. The method is explained in Chapter 1 Chemical Reactions and Equations of NCERT Class 10 Science is Hit and Trial Method. This is a simple way to balance equations.
This post explains all steps for balancing a chemical equation. This guide gives you a complete, exam ready method, multiple solved
examples, mistakes to avoid and practice examples.
Why must a Chemical Equation be Balanced?
A chemical reaction follows the ‘Law of Conservation of Mass’. According to this law “Atoms are neither created nor destroyed during a chemical reaction.”
Therefore, atoms of each element (in reactants and products) must be equal on the left-hand side and right-hand side of the equation.
Important Terms Related to Chemical Equation
First, you must know a few terms before learning balancing chemical equation.
· Skeletal Equation: An unbalanced equation showing only formula of reactants and products is called skeletal equation.
· Balanced Equation: An equation with equal numbers of atoms on both sides is called balanced equation.
· Coefficient: Number written before a formula.
· Subscript: Small number in a formula
Hit and Trial Methos (Step by step)
This method is an easy way to balance a chemical equation specially for class 9 and 10.
We will balance:
Fe + H2O → Fe3O4 + H2
Step 1- Draw boxes around the reactants and products
First of all, we draw boxes around the chemical formula given in the equation so that we do not touch the subscripts in the formula.
Step 2 – Count atoms
We count the numbers of atoms of each element on both sides.
|
Elements |
LHS |
RHS |
|
Fe |
1 |
3 |
|
H |
2 |
2 |
|
O |
1 |
4 |
Step 3 – Follow the MNOH Rule to balance
We will follow MNOH rule where:
M= metal
N = non-metal
O= oxygen
H = hydrogen
First of all, we balance metal on both sides, then non-metal, oxygen and hydrogen.
In the given Fe is a metal so we balance it first.
We put 3 before Fe on left hand side
3Fe + H2O → Fe3O4 + H2
There is no non metal in the equation, so we will balance
oxygen on both sides
We put 2 before 4 before H2O
3Fe + 4H2O → Fe3O4 + H2
Now in the last we will balance hydrogen
We put 4 before H2 on RHS
3Fe + 4H2O → Fe3O4 + 4H2
Now we recount all the elements on both sides
|
Elements |
LHS |
RHS |
|
Fe |
3 |
3 |
|
H |
8 |
8 |
|
O |
4 |
4 |
We can see all the elements have same numbers of atoms
on both sides so the equation is balanced now.
Balanced Chemical Equation
3Fe + 4H2O → Fe3O4 + 4H2
Golden rule to balance equation
i. Change coefficient but never change subscript
ii. Balance metal first, then non-metal, oxygen and hydrogen
iii. Use smallest whole numbers
iv. Recount atoms on both sides
v. Add state symbols if required
Solved Examples of Balanced Chemical Equations
After learning steps for balancing chemical equations, you can easily understand the following examples of chemical equations.
(i)Mg + O2→ MgO
2Mg + O2→ 2MgO
(ii) Al + O2 → Al2O3
4Al + 3O2 → 2Al2O3
(iii)Na + H2O → NaOH + H2
2Na + 2H2O → 2NaOH + H2
(iv)KClO3 → KCl + O2
2KClO3 → 2KCl + 3O2
(v)Zn + HCl →ZnCl2 +H2
Zn + 2HCl →ZnCl2 +H2
(vi)Pb(NO3)2 → PbO + NO2 +O2
2Pb(NO3)2 → 2PbO + 4NO2 +O2
(vii)BaCl2 + Na2SO4 →BaSO4 +NaCl
BaCl2 + Na2SO4 →BaSO4 +2NaCl
Special Tips for Balancing Different Types of Reactions
You can also follow the tips for special types of chemical reactions.
|
Type of Reaction |
Tips |
|
Combination reaction |
Balance Oxygen |
|
Decomposition reaction |
Balance oxygen |
|
Displacement reaction |
Balance the displaced |
|
Double displacement |
Treat polyatomic |
|
Redox reaction |
Balance oxygen |
Common Mistakes in Balancing Equation
Students sometimes make mistakes in balancing chemical equations. Avoid these mistakes:
· If you change subscript of any element, the formula of substance changes
· Do not forget to balance diatomic gases like H2, O2, Cl2
· Do not use fractions, always use whole numbers
· Always recount atoms
Practice Sets for Balancing Chemical Equations
You can try to balance the following chemical equations by the above method.
(i) H2 + Cl2 →HCl
(ii) Fe + O2 →Fe2O3
(iii) Ca + H2O →Ca(OH)2 + H2
(iv) N2 +H2 → NH3
(v) Al +HCl →AlCl3 H2
(vi) Na2CO3 +HCl →NaCl + H2 + CO2
(vii) Cu + O2 →CuO
(viii) Fe2O3 +Al →Al2O3+Fe
(ix) C2H6 + O2 →CO2+H2O
(x) NH3 +O2 →NO + H2O
(xi) AgNO3 + NaCl →AgCl + NaNO3
Conclusion
If you follow this Hit and Trail method carefully and practice daily, you can balance every chemical equation.
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