Practice at balancing
Using the inspection method, let us balance the five equations on page 94. Notice that only the coefficients change in each one.
| Unbalanced | Balanced equation |
|---|---|
| Na + O2 → Na2O | 4Na + O2 → 2Na2O |
| Al + O2 → Al2O3 | 4Al + 3O2 → 2Al2O3 |
| N2 + H2 → NH3 | N2 + 3H2 → 2NH3 |
| H2 + O2 → H2O | 2H2 + O2 → 2H2O |
| KClO3 → KCl + O2 | 2KClO3 → 2KCl + 3O2 |
Assignment 16.1
The problem
Write balanced chemical equations for the word equations, and state which type of reaction each equation belongs to.
| # | Balanced equation | Type |
|---|---|---|
| 1 a | 2Mg + O2 → 2MgO | combination |
| 1 b | Zn + CuSO4 → ZnSO4 + Cu | single displacement |
| 2 a | Mg + 2HCl → MgCl2 + H2 | single displacement |
| 2 b | FeSO4 + 2NaOH → Fe(OH)2 + Na2SO4 | double displacement |
| 3 a | CaCO3 → CaO + CO2 | decomposition |
| 3 b | Fe + S → FeS | combination |
| 4 a | CaCl2 + Na2CO3 → CaCO3 + 2NaCl | double displacement |
| 4 b | Fe2O3 + 3CO → 2Fe + 3CO2 | reduction — see the note below |
| 5 a | 4Na + O2 → 2Na2O | combination |
| 5 b | 2Na + 2H2O → 2NaOH + H2 | single displacement |
4 b does not fit the four types neatly
In Fe2O3 + 3CO both reactants are compounds, yet Fe appears as a lone element on the right — so it fits neither the single nor the double displacement pattern exactly. It is better described as a reduction: the CO removes oxygen from the Fe2O3. We meet it again when we come to the extraction of iron.
Show your answers to your teacher and confirm that they are right.