Chemistry worksheet answer key for word equations.

Let’s go through each word equation and convert it into a balanced chemical equation, step by step.

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1. Zinc and lead(II) nitrate react to form zinc nitrate and lead.

- Reactants: Zn (zinc metal), Pb(NO₃)₂ (lead(II) nitrate)
- Products: Zn(NO₃)₂ (zinc nitrate), Pb (lead metal)
- This is a single replacement reaction.
- Check atoms:
- Left: Zn=1, Pb=1, N=2, O=6
- Right: Zn=1, Pb=1, N=2, O=6 → already balanced!

✔ Balanced Equation:
Zn + Pb(NO₃)₂ → Zn(NO₃)₂ + Pb

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2. Aluminum bromide and chlorine gas react to form aluminum chloride and bromine gas.

- Reactants: AlBr₃, Cl₂
- Products: AlCl₃, Br₂
- Unbalanced: AlBr + Cl₂ → AlCl₃ + Br₂
- Balance Br first: need 2 AlBr₃ to get even number of Br atoms → 2AlBr₃
- Then we get 6 Br on left → need 3 Br₂ on right
- Now Al: 2 on left → need 2 AlCl₃ on right
- Now Cl: 2 AlCl₃ = 6 Cl atoms → need 3 Cl₂ on left

✔ Balanced Equation:
2AlBr₃ + 3Cl₂ → 2AlCl₃ + 3Br₂

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3. Sodium phosphate and calcium chloride react to form calcium phosphate and sodium chloride.

- Reactants: Na₃PO₄, CaCl₂
- Products: Ca₃(PO₄)₂, NaCl
- Unbalanced: Na₃PO₄ + CaCl₂ → Ca₃(PO₄)₂ + NaCl
- Balance PO₄: need 2 Na₃PO₄ to match 2 PO₄ in product
- Now Na: 6 on left → need 6 NaCl on right
- Now Cl: 6 on right → need 3 CaCl₂ on left (since each has 2 Cl)
- Now Ca: 3 on left → matches Ca₃(PO₄)₂ on right

✔ Balanced Equation:
2Na₃PO₄ + 3CaCl₂ → Ca₃(PO₄)₂ + 6NaCl

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4. Potassium metal and chlorine gas combine to form potassium chloride.

- Reactants: K, Cl₂
- Product: KCl
- Unbalanced: K + Cl₂ → KCl
- Need 2 K and 2 KCl to balance Cl₂

✔ Balanced Equation:
2K + Cl₂ → 2KCl

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5. Aluminum and hydrochloric acid react to form aluminum chloride and hydrogen gas.

- Reactants: Al, HCl
- Products: AlCl₃, H₂
- Unbalanced: Al + HCl → AlCl₃ + H₂
- Balance Cl: need 3 HCl for one AlCl₃ → but then H is odd
- Try 2 Al → need 2 AlCl₃ → need 6 HCl → gives 6 H → makes 3 H₂

✔ Balanced Equation:
2Al + 6HCl → 2AlCl₃ + 3H₂

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6. Calcium hydroxide and phosphoric acid react to form calcium phosphate and water.

- Reactants: Ca(OH)₂, H₃PO₄
- Products: Ca₃(PO₄)₂, H₂O
- Unbalanced: Ca(OH)₂ + H₃PO₄ → Ca₃(PO₄)₂ + H₂O
- Balance Ca: need 3 Ca(OH)₂
- Balance PO₄: need 2 H₃PO₄
- Now check H and O:
- Left: from 3 Ca(OH)₂ → 6 OH → 6 H, 6 O; from 2 H₃PO₄ → 6 H, 8 O → total H=12, O=14
- Right: Ca₃(PO₄)₂ has no H or extra O; water must take all H and remaining O
- 12 H → need 6 H₂O → which uses 6 O → leftover O? Wait — let’s count again.

Actually:

Left:
- 3 Ca(OH)₂ → 3 Ca, 6 O, 6 H
- 2 H₃PO₄ → 6 H, 2 P, 8 O
→ Total: Ca=3, P=2, H=12, O=14

Right:
- Ca₃(PO₄)₂ → 3 Ca, 2 P, 8 O
- Water: need to account for 12 H and 6 more O → so 6 H₂O (which is 12 H, 6 O)

Perfect!

✔ Balanced Equation:
3Ca(OH)₂ + 2H₃PO₄ → Ca₃(PO₄)₂ + 6H₂O

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7. Copper and sulfuric acid react to form copper(II) sulfate and water and sulfur dioxide.

- Reactants: Cu, H₂SO₄
- Products: CuSO₄, H₂O, SO₂
- Note: This is not typical dilute acid reaction — concentrated H₂SO₄ reacts with Cu to give SO₂.
- Unbalanced: Cu + H₂SO₄ → CuSO₄ + H₂O + SO₂
- Let’s try balancing:
- Cu: 1 on both sides
- S: left=1, right=2 (one in CuSO, one in SO₂) → need 2 H₂SO₄ on left
- Now H: 4 on left → need 2 H₂O on right
- O: left=8 (from 2 H₂SO₄), right: CuSO₄=4, 2 H₂O=2, SO₂=2 → total 8 → good!

✔ Balanced Equation:
Cu + 2H₂SO₄ → CuSO₄ + 2H₂O + SO₂

*(Note: Some sources write this as requiring heat, but for balancing purposes, this works.)*

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8. Hydrogen gas and nitrogen monoxide react to form water and nitrogen gas.

- Reactants: H₂, NO
- Products: H₂O, N₂
- Unbalanced: H₂ + NO → H₂O + N₂
- Balance N: need 2 NO to make N₂
- Now O: 2 on left → need 2 H₂O on right
- Now H: 4 on right → need 2 H₂ on left

✔ Balanced Equation:
2H₂ + 2NO → 2H₂O + N₂

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Final Answer:

1. Zn + Pb(NO₃)₂ → Zn(NO₃)₂ + Pb
2. 2AlBr₃ + 3Cl₂ → 2AlCl₃ + 3Br₂
3. 2Na₃PO₄ + 3CaCl₂ → Ca₃(PO₄)₂ + 6NaCl
4. 2K + Cl₂ → 2KCl
5. 2Al + 6HCl → 2AlCl₃ + 3H₂
6. 3Ca(OH)₂ + 2H₃PO₄ → Ca₃(PO₄)₂ + 6H₂O
7. Cu + 2H₂SO₄ → CuSO₄ + 2H₂O + SO₂
8. 2H₂ + 2NO → 2H₂O + N₂