Balanced chemical equations for common chemical reactions.

Let’s go through each reaction one by one and write the balanced chemical equation. I’ll make sure atoms of each element are equal on both sides.

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1. Zinc reacts with hydrogen chloride to form zinc chloride + hydrogen gas

Unbalanced:
Zn + HCl → ZnCl₂ + H₂

Check atoms:
- Left: Zn=1, H=1, Cl=1
- Right: Zn=1, H=2, Cl=2 → Not balanced!

Fix: Put 2 in front of HCl
→ Zn + 2HCl → ZnCl₂ + H₂

Now check:
- Left: Zn=1, H=2, Cl=2
- Right: Zn=1, Cl=2, H=2 → ✔ Balanced!

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2. Sodium oxide reacts with water to form sodium hydroxide

Unbalanced:
Na₂O + H₂O → NaOH

Left: Na=2, O=2 (1 from Na₂O + 1 from H₂O), H=2
Right: Na=1, O=1, H=1 → Not balanced!

Put 2 in front of NaOH:
Na₂O + H₂O → 2NaOH

Check:
- Left: Na=2, O=2, H=2
- Right: Na=2, O=2, H=2 → ✔ Balanced!

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3. Iron metal reacts with water to form Fe₃O₄ and hydrogen gas

Unbalanced:
Fe + H₂O → Fe₃O₄ + H₂

Left: Fe=1, H=2, O=1
Right: Fe=3, O=4, H=2 → Not balanced!

Need 3 Fe on left → put 3 in front of Fe
Need 4 O on left → need 4 H₂O (since each has 1 O)
So: 3Fe + 4H₂O → Fe₃O₄ + H₂

Now check H: Left = 8 H (from 4 H₂O), Right = 2 H → Need 4 H₂ on right

Final:
3Fe + 4H₂O → Fe₃O₄ + 4H₂

Check:
- Fe: 3 = 3
- O: 4 = 4
- H: 8 = 8 → ✔ Balanced!

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4. Aluminum bromide reacts with chlorine gas to produce aluminum chloride and liquid bromine

Aluminum bromide = AlBr₃
Chlorine gas = Cl₂
Aluminum chloride = AlCl₃
Bromine liquid = Br₂

Unbalanced:
AlBr₃ + Cl₂ → AlCl₃ + Br₂

Left: Al=1, Br=3, Cl=2
Right: Al=1, Cl=3, Br=2 → Not balanced!

Find LCM for Br: 3 and 2 → use 6
So: 2AlBr₃ + ?Cl₂ → 2AlCl₃ + 3Br₂

Now Br: 6 = 6
Al: 2 = 2
Cl: right = 6 → so left needs 3 Cl₂ (since 3×2=6)

Final:
2AlBr₃ + 3Cl₂ → 2AlCl₃ + 3Br₂

Check:
- Al: 2=2
- Br: 6=6
- Cl: 6=6 → ✔ Balanced!

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5. Nitric acid (HNO₃) reacts with barium hydroxide to produce barium nitrate and water

Barium hydroxide = Ba(OH)₂
Barium nitrate = Ba(NO₃)₂
Water = H₂O

Unbalanced:
HNO₃ + Ba(OH)₂ → Ba(NO₃)₂ + H₂O

Left: H=1+2=3? Wait — better to count per molecule.

Actually:
HNO₃ has H=1, N=1, O=3
Ba(OH)₂ has Ba=1, O=2, H=2
Total left: H=3, N=1, O=5, Ba=1

Right: Ba(NO₃)₂ → Ba=1, N=2, O=6; H₂O → H=2, O=1 → total H=2, O=7, N=2, Ba=1 → not balanced!

We need 2 HNO₃ to get 2 N on left → matches Ba(NO₃)₂

Try:
2HNO₃ + Ba(OH)₂ → Ba(NO₃)₂ + H₂O

Now left: H=2+2=4, N=2, O=6+2=8, Ba=1
Right: Ba=1, N=2, O=6 + ? from H₂O → if we put 2 H₂O → H=4, O=2 → total O=8

Yes!
2HNO₃ + Ba(OH)₂ → Ba(NO₃)₂ + 2H₂O

Check:
- H: 2+2=4 vs 4 → ok
- N: 2=2
- O: 6+2=8 vs 6+2=8
- Ba: 1=1 → ✔ Balanced!

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6. Calcium sulfite decomposes when heated to form calcium oxide and sulfur dioxide

Calcium sulfite = CaSO₃
Calcium oxide = CaO
Sulfur dioxide = SO₂

Unbalanced:
CaSO₃ → CaO + SO₂

Check atoms:
Left: Ca=1, S=1, O=3
Right: Ca=1, S=1, O=1+2=3 → ✔ Already balanced!

So:
CaSO₃ → CaO + SO₂

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7. Iron reacts with sulfuric acid (H₂SO₄) to form iron (II) sulfate and hydrogen gas

Iron (II) sulfate = FeSO₄
Hydrogen gas = H₂

Unbalanced:
Fe + H₂SO₄ → FeSO₄ + H₂

Check:
Left: Fe=1, H=2, S=1, O=4
Right: Fe=1, S=1, O=4, H=2 → ✔ Already balanced!

So:
Fe + H₂SO₄ → FeSO₄ + H₂

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8. Ammonia (NH₃) burns in air to form nitrogen dioxide and water

Air provides oxygen → O₂
Nitrogen dioxide = NO₂
Water = H₂O

Unbalanced:
NH₃ + O₂ → NO₂ + H₂O

Left: N=1, H=3, O=2
Right: N=1, O=2+1=3? Wait — NO₂ has 2 O, H₂O has 1 O → total 3 O, but H=2 → not matching H=3

Need to balance H first. LCM of 3 and 2 is 6.

So: 2NH₃ → gives 6 H → need 3 H₂O (which has 6 H)

Then N: 2N → need 2NO₂

Now: 2NH₃ + O₂ → 2NO₂ + 3H₂O

Check O: right = 2×2 + 3×1 = 4+3=7 O → left must have 7 O → so O₂ coefficient = 7/2 → not whole number

Multiply entire equation by 2:

4NH₃ + 7O₂ → 4NO₂ + 6H₂O

Check:
N: 4=4
H: 12=12
O: 14 = 8 + 6 = 14 → ✔ Balanced!

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9. Carbon disulfide burns in air to form carbon dioxide and sulfur dioxide

Carbon disulfide = CS₂
Oxygen from air = O₂
CO₂ and SO₂

Unbalanced:
CS₂ + O₂ → CO₂ + SO₂

Left: C=1, S=2, O=2
Right: C=1, S=1, O=2+2=4 → not balanced!

Need 2 SO₂ to match S=2

So: CS₂ + O₂ → CO₂ + 2SO₂

Now S: 2=2
C: 1=1
O: right = 2 + 4 = 6 → left needs 3 O₂ (since 3×2=6)

Final:
CS₂ + 3O₂ → CO₂ + 2SO₂

Check:
C:1=1, S:2=2, O:6=6 → ✔ Balanced!

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Final Answer:

1. Zn + 2HCl → ZnCl₂ + H₂
2. Na₂O + H₂O → 2NaOH
3. 3Fe + 4H₂O → Fe₃O₄ + 4H₂
4. 2AlBr₃ + 3Cl₂ → 2AlCl₃ + 3Br₂
5. 2HNO₃ + Ba(OH)₂ → Ba(NO₃)₂ + 2H₂O
6. CaSO₃ → CaO + SO₂
7. Fe + H₂SO₄ → FeSO₄ + H₂
8. 4NH₃ + 7O₂ → 4NO₂ + 6H₂O
9. CS₂ + 3O₂ → CO₂ + 2SO₂