Question 1
Can you change H₂O to H₂O₂ to balance an equation? Explain.
Need a hint for Question 1?
Use the relationships above and check particle ratios and units.
Check Question 1
No. It changes the substance. Change coefficients only.
STUDENT SPACE · TOPIC 2
Balanced and ionic equations
Balance equations, add state symbols and remove spectator ions.
The essentials
- Two H₂ molecules react with one O₂ molecule to form two H₂O molecules.
- Change coefficients, never the formulae of the substances.
- Al + O₂ → Al₂O₃: use 6 oxygen atoms on each side.
- 4Al + 3O₂ → 2Al₂O₃: now both Al and O balance.
Key vocabulary
| English | Chinese |
|---|---|
| coefficient | 化学计量数 |
| state symbol | 状态符号 |
| spectator ion | 旁观离子 |
Quick practice
Try each question before opening its hint or answer. Use paper for calculations and diagrams.
Question 2
Balance: Fe(s) + O₂(g) → Fe₂O₃(s).
Need a hint for Question 2?
Balance oxygen using a common multiple of two and three.
Check Question 2
4Fe(s) + 3O₂(g) → 2Fe₂O₃(s).
Question 3
Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s). Check the atoms and total charge on each side.
Need a hint for Question 3?
Check atom counts and charge totals independently.
Check Question 3
One Zn and one Cu on each side; total charge +2 on each side.
Use Lesson 2 in your worksheet for written practice. Your teacher will discuss those answers in class.