Steps to Balance a Chemical Equation
To balance a chemical equation, follow these systematic steps:
- Identify the reactants and products, and write the molecular formula for each.
- Express the equation by placing the reactants before the arrow and the products after the arrow.
- Count the number of atoms for each element in both the reactants and the products.
- If the equation is unbalanced, adjust the coefficients of the molecules so that the number of atoms for each element in the reactants equals that in the products.
- Verify the atom counts to ensure that the equation is balanced.
- Add any additional information to the equation, such as the physical states of the substances.
Examples of Balancing Chemical Equations
Example 1
Consider the equation representing the rusting of iron in the presence of air. How is this equation balanced?
Step one: Write the unbalanced equation as follows:
Fe + O2 → Fe2O3, ensuring to place the reactants on the left side of the arrow and the products on the right.
Step two: Count the atoms for each element in the reactants as follows:
- Iron: 1 atom.
- Oxygen: 2 atoms.
Next, count the atoms in the products:
- Iron: 2 atoms.
- Oxygen: 3 atoms.
Step three: To balance the iron atoms, start by thinking about multiplying the reactant by 2 to match the product. However, this also does not balance the oxygen. After further exploration, if you multiply Fe by 4 and Fe2O3 by 2, the iron atoms in both the reactants and products become equal, resulting in the following equation:
4Fe + O2 → 2 Fe2O3
Step four: Next, balance the oxygen atoms by adding a coefficient of 3 to the molecule O2, leading to a balanced number of oxygen atoms in both the reactants and products, which totals 6. The final balanced equation now reads:
4Fe + 3 O2 → 2 Fe2O3
Example 2
Consider this chemical equation:
N2(g) + O2(g) → NO2(g)
Solution:
By applying the steps for balancing chemical equations, the balanced form of this equation is:
N2(g) + 2O2(g) → 2NO2(g)