Balancing Chemical Equation

• Law of Conservation of Mass: In a chemical reaction, mass is neither created nor destroyed, so the number of atoms of each element must be equal on both sides.
• A skeletal (unbalanced) equation has unequal atoms of one or more elements on the LHS and RHS.
• Balancing is done using the hit-and-trial method, starting with the compound having the most atoms and balancing hydrogen and oxygen last.
• Only coefficients are changed while balancing; chemical formulas must not be altered.
• A balanced equation may also indicate physical states (s, l, g, aq) and reaction conditions, such as temperature, pressure, or a catalyst.

When a chemical reaction occurs, the mass of the reactants must be equal to the mass of the products. This follows from the Law of Conservation of Mass, which states that matter cannot be created or destroyed in a chemical reaction. A balanced chemical equation ensures that the number of atoms of each element is equal on both sides of the equation.

Example 1:

Balancing the Reaction of Iron with Steam

Step 1: Write the Unbalanced Chemical Equation

Fe + H₂O → Fe₃O₄ + H₂​

Step 2: Count the Number of Atoms of Each Element

Step 3: Balance the Oxygen Atoms

There are 4 oxygen atoms in Fe₃O₄ but only 1 in H₂O. To balance, multiply H₂O by 4:

Fe + 4H₂O → Fe₃O₄ + H₂​

Step 4: Balance the Hydrogen Atoms

Now, there are 8 hydrogen atoms in 4 H₂O, but only 2 in H₂. Multiply H₂ by 4 to balance:

Fe + 4H₂O → Fe₃O₄ + 4H₂​

Step 5: Balance the Iron Atoms

On the RHS, Fe₃O₄ contains 3 Fe atoms, but on the LHS, there is only 1 Fe. Multiply Fe by 3:

3Fe + 4H₂O → Fe₃O₄ + 4H₂​

Step 6: Verify the Balanced Equation

Now, the equation is balanced.

Step 7: Indicate Physical States

3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)

Example 2:

Balancing the Reaction of Sodium Hydroxide with Sulfuric Acid

Step 1: Write the Unbalanced Chemical Equation

NaOH + H₂SO₄ → Na₂SO₄ + H₂O

Step 2: Count the Number of Atoms of Each Element

Step 3: Balance the Sodium (Na) Atoms

Na₂SO₄ contains 2 Na atoms, but there is only 1 Na in NaOH. Multiply NaOH by 2:

2NaOH + H₂SO₄ → Na₂SO₄ + H₂O₂

Step 4: Balance the Hydrogen Atoms

There are 4 hydrogen atoms in reactants (from NaOH and H₂SO₄) but only 2 in H₂O. Multiply H₂O by 2 to balance:

2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O₂

Step 5: Verify the Balanced Equation

Now, the equation is balanced.

Step 6: Indicate Physical States

2NaOH(aq) + H₂SO₄(aq) → Na₂SO₄(aq) + 2H₂O(l)