How to balance a chemical equation?

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Balancing a chemical equation ensures that the Law of Conservation of Mass is followed, meaning the number of atoms of each element must be the same on both the reactant and product sides of the equation.

To systematically balance a chemical equation, follow these steps:

Step-by-Step Method to Balance Chemical Equations

  1. Write the Unbalanced Equation:
    Write the chemical equation with the correct formulas for reactants and products. For example:Fe+O2→Fe2O3Fe+O2​→Fe2​O3​
  2. Count the Atoms of Each Element:
    Count the number of atoms of each element on both sides of the equation.
    • Reactants: Fe = 1, O = 2
    • Products: Fe = 2, O = 3
  3. Balance Metals First:
    Start with the metal atoms because they usually appear in fewer compounds and are easier to balance.
    • In the example, balance Fe by placing a coefficient of 2 in front of Fe on the reactant side:2Fe+O2→Fe2O32Fe+O2​→Fe2​O3​
    • Now, Fe is balanced: Fe = 2 on both sides.
  4. Balance Non-Metals (Except Hydrogen and Oxygen):
    Next, balance non-metals like sulfur, nitrogen, etc., if present. In this example, there are no non-metals other than oxygen.
  5. Balance Oxygen:
    Balance oxygen atoms by adjusting coefficients. In the example:
    • Reactants: O = 2
    • Products: O = 3
    • To balance oxygen, find the least common multiple (LCM) of 2 and 3, which is 6.
    • Place a coefficient of 3 in front of O₂ and 2 in front of Fe₂O₃:2Fe+3O2→2Fe2O32Fe+3O2​→2Fe2​O3​
    • Now, O is balanced: O = 6 on both sides.
  6. Balance Hydrogen:
    If hydrogen is present, balance it after oxygen. For example:H2+O2→H2OH2​+O2​→H2​O
    • Balance H by placing a coefficient of 2 in front of H₂O:H2+O2→2H2OH2​+O2​→2H2​O
    • Now, balance O by placing a coefficient of 2 in front of O₂:2H2+O2→2H2O2H2​+O2​→2H2​O
  7. Double-Check All Atoms:
    Ensure that all elements are balanced on both sides of the equation.

Example 1: Combustion of Methane

Unbalanced equation:CH4+O2→CO2+H2OCH4​+O2​→CO2​+H2​O

  1. Balance C:
    • C is already balanced (1 on both sides).
  2. Balance H:
    • Place a coefficient of 2 in front of H₂O:CH4+O2→CO2+2H2OCH4​+O2​→CO2​+2H2​O
    • Now, H is balanced (4 on both sides).
  3. Balance O:
    • Reactants: O = 2
    • Products: O = 2 (from CO₂) + 2 (from H₂O) = 4
    • Place a coefficient of 2 in front of O₂:CH4+2O2→CO2+2H2OCH4​+2O2​→CO2​+2H2​O
    • Now, O is balanced (4 on both sides).

Example 2: Reaction of Sodium with Water

Unbalanced equation:Na+H2O→NaOH+H2Na+H2​O→NaOH+H2​

  1. Balance Na:
    • Place a coefficient of 2 in front of Na and NaOH:2Na+H2O→2NaOH+H22Na+H2​O→2NaOH+H2​
    • Now, Na is balanced (2 on both sides).
  2. Balance H:
    • Reactants: H = 2
    • Products: H = 2 (from NaOH) + 2 (from H₂) = 4
    • Place a coefficient of 2 in front of H₂O:2Na+2H2O→2NaOH+H22Na+2H2​O→2NaOH+H2​
    • Now, H is balanced (4 on both sides).
  3. Balance O:
    • O is already balanced (2 on both sides).

General Order of Balancing

  1. Metals
  2. Non-metals (except H and O)
  3. Oxygen
  4. Hydrogen

By following this method, you can systematically balance any chemical equation. Practice with more examples to become proficient!

Here are 10 practice questions covering different types of chemical reactions. These include synthesis, decomposition, single displacement, double displacement, and combustion reactions. Try balancing each equation step by step!

1. Synthesis Reaction

Balance the following synthesis reaction:Mg+O2→MgOMg+O2​→MgO

2. Decomposition Reaction

Balance the following decomposition reaction:H2O2→H2O+O2H2​O2​→H2​O+O2​

3. Single Displacement Reaction

Balance the following single displacement reaction:Zn+HCl→ZnCl2+H2Zn+HCl→ZnCl2​+H2​

4. Double Displacement Reaction

Balance the following double displacement reaction:AgNO3+NaCl→AgCl+NaNO3AgNO3​+NaCl→AgCl+NaNO3​

5. Combustion Reaction

Balance the following combustion reaction:C3H8+O2→CO2+H2OC3​H8​+O2​→CO2​+H2​O

6. Redox Reaction

Balance the following redox reaction:Fe2O3+CO→Fe+CO2Fe2​O3​+CO→Fe+CO2​

7. Reaction with Polyatomic Ions

Balance the following reaction involving polyatomic ions:Ca(OH)2+H3PO4→Ca3(PO4)2+H2OCa(OH)2​+H3​PO4​→Ca3​(PO4​)2​+H2​O

8. Complex Reaction

Balance the following complex reaction:KClO3→KCl+O2KClO3​→KCl+O2​

9. Reaction with Multiple Elements

Balance the following reaction:NH3+O2→NO+H2ONH3​+O2​→NO+H2​O

10. Reaction with Fractions

Balance the following reaction (hint: use fractions if needed):C2H6+O2→CO2+H2OC2​H6​+O2​→CO2​+H2​O

Answers (Balanced Equations):

  1. Synthesis Reaction:2Mg+O2→2MgO2Mg+O2​→2MgO
  2. Decomposition Reaction:2H2O2→2H2O+O22H2​O2​→2H2​O+O2​
  3. Single Displacement Reaction:Zn+2HCl→ZnCl2+H2Zn+2HCl→ZnCl2​+H2​
  4. Double Displacement Reaction:AgNO3+NaCl→AgCl+NaNO3AgNO3​+NaCl→AgCl+NaNO3​(Already balanced)
  5. Combustion Reaction:C3H8+5O2→3CO2+4H2OC3​H8​+5O2​→3CO2​+4H2​O
  6. Redox Reaction:Fe2O3+3CO→2Fe+3CO2Fe2​O3​+3CO→2Fe+3CO2​
  7. Reaction with Polyatomic Ions:3Ca(OH)2+2H3PO4→Ca3(PO4)2+6H2O3Ca(OH)2​+2H3​PO4​→Ca3​(PO4​)2​+6H2​O
  8. Complex Reaction:2KClO3→2KCl+3O22KClO3​→2KCl+3O2​
  9. Reaction with Multiple Elements:4NH3+5O2→4NO+6H2O4NH3​+5O2​→4NO+6H2​O
  10. Reaction with Fractions:2C2H6+7O2→4CO2+6H2O2C2​H6​+7O2​→4CO2​+6H2​O(Alternatively, using fractions: C2H6+72O2→2CO2+3H2OC2​H6​+27​O2​→2CO2​+3H2​O)

Practice these questions to master balancing chemical equations! Let me know if you need further clarification. 

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