GCSE Chemistry balancing equations worksheet with various chemical reactions to balance.

Let's go through each chemical equation one by one and balance them. Balancing chemical equations involves ensuring that the number of atoms of each element is the same on both sides of the equation (following the Law of Conservation of Mass).

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1. Na + Cl₂ → NaCl

Unbalanced:
Na + Cl₂ → NaCl

- Left: 1 Na, 2 Cl
- Right: 1 Na, 1 Cl

We need 2 Cl on the right, so put 2 NaCl:
- Now right has: 2 Na, 2 Cl
- But left only has 1 Na → add 2 Na on the left.

✔ Balanced:
2Na + Cl₂ → 2NaCl

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2. Mg + HCl → MgCl₂ + H₂

Unbalanced:
Mg + HCl → MgCl₂ + H₂

- Left: 1 Mg, 1 H, 1 Cl
- Right: 1 Mg, 2 Cl, 2 H

We need 2 Cl and 2 H on the left → use 2 HCl

✔ Balanced:
Mg + 2HCl → MgCl₂ + H₂

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3. H₂ + O₂ → H₂O

Unbalanced:
H₂ + O₂ → H₂O

- Left: 2 H, 2 O
- Right: 2 H, 1 O

Need 2 O on the right → use 2 H₂O
- Now right: 4 H, 2 O
- Left: 2 H, 2 O → need more H₂ → use 2 H₂

✔ Balanced:
2H₂ + O₂ → 2H₂O

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4. Fe + Cl₂ → FeCl₃

Unbalanced:
Fe + Cl₂ → FeCl₃

- Left: 1 Fe, 2 Cl
- Right: 1 Fe, 3 Cl

To balance Cl: LCM of 2 and 3 is 6 → use 3 Cl₂ (6 Cl) and 2 FeCl₃ (6 Cl)

Now Fe: right has 2 Fe → need 2 Fe on left

✔ Balanced:
2Fe + 3Cl₂ → 2FeCl₃

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5. H₂O₂ → O₂ + H₂O

Unbalanced:
H₂O₂ → O₂ + H₂O

- Left: 2 H, 2 O
- Right: 2 O (from O₂), 2 H, 1 O (from H₂O) → total 3 O → too many

Better to think: decomposition of hydrogen peroxide.

We know it decomposes as:
2H₂O₂ → O₂ + 2H₂O

Check:
- Left: 4 H, 4 O
- Right: O₂ = 2 O, 2H₂O = 4 H, 2 O → total 4 H, 4 O

✔ Balanced:
2H₂O₂ → O₂ + 2H₂O

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6. Ca + H₂O → Ca(OH)₂ + H₂

Unbalanced:
Ca + H₂O → Ca(OH)₂ + H₂

- Left: 1 Ca, 2 H, 1 O
- Right: 1 Ca, 2 O, 2 H (in OH), plus 2 H in H₂ → total 4 H, 2 O

So oxygen: left has 1 O, right has 2 O → need 2 H₂O

Try:
Ca + 2H₂O → Ca(OH)₂ + H₂

Now:
- Left: 1 Ca, 4 H, 2 O
- Right: Ca(OH)₂ → 1 Ca, 2 O, 2 H; H₂ → 2 H → total 4 H, 2 O, 1 Ca

✔ Balanced:
Ca + 2H₂O → Ca(OH)₂ + H₂

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7. Ca + HNO₃ → Ca(NO₃)₂ + H₂

Unbalanced:
Ca + HNO₃ → Ca(NO₃)₂ + H₂

- Left: 1 Ca, 1 H, 1 N, 3 O
- Right: 1 Ca, 2 N, 6 O, 2 H

Need 2 NO₃ groups → use 2 HNO₃

Then:
Ca + 2HNO₃ → Ca(NO₃)₂ + H₂

Now check:
- Left: 1 Ca, 2 H, 2 N, 6 O
- Right: 1 Ca, 2 N, 6 O, 2 H

✔ Balanced:
Ca + 2HNO₃ → Ca(NO₃)₂ + H₂

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8. Ca + H₃PO₄ → Ca₃(PO₄)₂ + H₂

Wait — you wrote H₃POₓ, but likely meant H₃PO₄ (phosphoric acid). Also, product is Ca₃(PO₄)₂ (calcium phosphate).

So correct reaction:
Ca + H₃PO₄ → Ca₃(PO₄)₂ + H₂

Now balance:

First, note:
- Ca₃(PO₄)₂ has 3 Ca and 2 PO₄ groups
- So we need 3 Ca and 2 H₃PO₄

Try:
3Ca + 2H₃PO₄ → Ca₃(PO₄)₂ + H₂

Now check atoms:
- Left: 3 Ca, 6 H, 2 P, 8 O
- Right: Ca₃(PO₄)₂ → 3 Ca, 2 P, 8 O; H₂ → 2 H → but we have 6 H on left!

So H₂ should be 3H₂ (6 H)

✔ Balanced:
3Ca + 2H₃PO₄ → Ca₃(PO₄)₂ + 3H₂

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✔ Final Balanced Equations:

| Original | Balanced |
|--------|---------|
| Na + Cl₂ → NaCl | 2Na + Cl₂ → 2NaCl |
| Mg + HCl → MgCl₂ + H₂ | Mg + 2HCl → MgCl₂ + H₂ |
| H₂ + O₂ → H₂O | 2H₂ + O₂ → 2H₂O |
| Fe + Cl₂ → FeCl₃ | 2Fe + 3Cl₂ → 2FeCl₃ |
| H₂O₂ → O₂ + H₂O | 2H₂O₂ → O₂ + 2H₂O |
| Ca + H₂O → Ca(OH)₂ + H₂ | Ca + 2H₂O → Ca(OH)₂ + H₂ |
| Ca + HNO₃ → Ca(NO₃)₂ + H₂ | Ca + 2HNO₃ → Ca(NO₃)₂ + H₂ |
| Ca + H₃PO₄ → Ca₃(PO₄)₂ + H₂ | 3Ca + 2H₃PO₄ → Ca₃(PO₄)₂ + 3H₂ |

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🔍 Summary Tips for Balancing:

1. Start with elements that appear only once on each side.
2. Balance metals first, then non-metals, then H and O last.
3. Use coefficients (numbers in front), not subscripts.
4. Check atom counts after each step.

Let me know if you'd like a visual guide or practice problems!