Balancing chemical equations is done to reflect the conservation of mass and to enable accurate quantitative analysis of a reaction. When equations are balanced, the same number of each type of atom appears on both sides, which lets chemists predict how much reactant is needed and how much product will form (stoichiometry). Key reasons

• Law of conservation of mass: Atoms are neither created nor destroyed in chemical reactions, so the total count of each element must be the same before and after the reaction. This is the primary rationale for balancing.

• Accurate stoichiometry: Balanced equations establish the correct mole ratios between reactants and products, enabling calculation of amounts required or produced in a reaction. This is essential for planning experiments, optimizing yields, and scaling reactions.

• Predicting quantities: Once balanced, coefficients give the molar relationships, which translate to mass relationships when combined with molar masses. This allows determination of limiting reagents, theoretical yields, and required quantities for desired outputs.

How balancing works (high level)

• Start with an unbalanced equation showing the reactants on the left and products on the right.
• Adjust the coefficients in front of the formulas (not the subscripts inside formulas) to equalize the number of each type of atom on both sides.
• Check that all elements are balanced and that the smallest possible whole-number coefficients are used. In some cases, fractional coefficients are temporarily introduced and then cleared by multiplying all coefficients by a common factor.

Common methods

• Inspection: For simple reactions, balance atoms by eye, starting with elements that appear in only one reactant and one product.

• Algebraic method: Set up a system of linear equations based on atom counts for each element and solve for coefficients.

Illustrative example

• Unbalanced methane combustion: CH4 + O2 → CO2 + H2O
• Balanced form: CH4 + 2 O2 → CO2 + 2 H2O
• Here, the coefficients 1, 2, 1, and 2 ensure equal numbers of C, H, and O atoms on both sides, reflecting mass conservation and giving the correct mole ratios for practical quantities.

If you’d like, I can walk through balancing a specific equation you’re working with and show each step, including the resulting mole and mass calculations.