Balancing chemical equations shows how reactants rearrange to form products while keeping the same number of each type of atom. Students need this skill to understand reactions, conservation of mass, and later stoichiometry problems. This cheat sheet gives a clear step-by-step method for turning an unbalanced skeleton equation into a balanced chemical equation.
Key Facts
- A chemical equation is balanced when each element has the same number of atoms on the reactant side and the product side.
- Coefficients multiply every atom in the formula that follows, so contains hydrogen atoms and oxygen atoms.
- Subscripts are part of a chemical formula and must not be changed when balancing, so cannot become .
- Start balancing with elements that appear in only one reactant and one product before balancing elements that appear in several compounds.
- Balance oxygen and hydrogen near the end because they often appear in multiple compounds, especially in combustion reactions.
- If a coefficient creates fractions, multiply every coefficient in the equation by the denominator, such as changing into whole-number coefficients.
- The balanced equation has hydrogen atoms and oxygen atoms on both sides.
- A balanced equation uses the smallest whole-number coefficients, such as instead of .
Vocabulary
- Reactant
- A reactant is a starting substance written on the left side of a chemical equation.
- Product
- A product is a substance formed by a reaction and written on the right side of a chemical equation.
- Coefficient
- A coefficient is a whole number placed before a formula to show how many units of that substance are involved.
- Subscript
- A subscript is a small number in a chemical formula that shows how many atoms of an element are in one unit of the substance.
- Conservation of Mass
- Conservation of mass means atoms are not created or destroyed during a chemical reaction.
- Skeleton Equation
- A skeleton equation shows the correct formulas for reactants and products before coefficients are added to balance it.
Common Mistakes to Avoid
- Changing subscripts to balance an equation is wrong because it changes the identity of the substance, such as turning into .
- Forgetting that coefficients multiply the entire formula is wrong because contains aluminum atoms and oxygen atoms, not aluminum atoms and oxygen atoms.
- Balancing oxygen or hydrogen first in a complex equation can make the process harder because these elements often appear in several compounds.
- Leaving fractional coefficients in the final answer is usually wrong because balanced equations should use the smallest whole-number coefficients.
- Stopping after one element balances is wrong because every element must be checked on both sides before the equation is complete.
Practice Questions
- 1 Balance the equation .
- 2 Balance the equation .
- 3 Balance the combustion equation .
- 4 Explain why changing to is not an acceptable way to balance an equation.