08. Balancing equations

• An equation is balanced when there are the same number of atoms of each type on both sides of the equation.

• An equation can only be balanced by putting numbers in front of formulas – you cannot change the formula itself.

• Equations can be written with state symbols: (s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous (dissolved in water).

How to balance an equation:

a) Calculate how many atoms of each type are on each side of the equation.

b) If the numbers are the same then the equation is balanced.

c) If the numbers are not the same, then numbers are put in front of the formulas (this adds more of that substance). You cannot change the formulas (this would make a different substance). Hint – start with unbalanced elements that only appear in one substance on each side of the equation.

d) Keep doing this until the equation is balanced. e.g. CH₄ + O₂ → CO₂ + H₂O

Get a spare piece of paper and try to balance the following:

1. Ca + O₂ → CaO

2. Na₂O + H₂O → NaOH

3. Al + O₂ → Al₂O₃

4. Na + Cl₂ → NaCl

5. Na₂CO₃ → Na₂O + CO₂

6. K + O₂ → K₂O

7. C₄H₈ + O₂ → CO₂ + H₂O

8. Fe₂O₃ + HCl → FeCl₃ + H₂O

9. F₂ + KBr → KF + Br₂

10. C₅H₁₂ + O₂ → CO₂ + H₂O

11. NH₃ + O₂ → NO + H₂O

12. HNO₃ → NO₂ + H₂O + O₂

thanks to www.chemsheets.co.uk for the questions and resources