Grade 7 Balancing Chemical Equations Answer Key Worksheets 2024 - Free Printable

Let’s go step by step to balance each chemical equation. Balancing means making sure the number of atoms of each element is the same on both sides of the arrow.

We’ll use coefficients (numbers in front) to balance — never change subscripts!

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1. Zn + AgNO₃ → Zn(NO₃)₂ + Ag

Left: Zn=1, Ag=1, N=1, O=3
Right: Zn=1, Ag=1, N=2, O=6 → Not balanced

Put 2 in front of AgNO₃ and 2 in front of Ag:

→ Zn + 2AgNO₃ → Zn(NO₃)₂ + 2Ag

Check:
Left: Zn=1, Ag=2, N=2, O=6
Right: Zn=1, Ag=2, N=2, O=6 ✔

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2. N₂ + H₂ → NH₃

Left: N=2, H=2
Right: N=1, H=3

Need 2 NH₃ to get 2N → then H=6 on right → need 3 H₂ on left

→ N₂ + 3H₂ → 2NH₃

Check: N=2, H=6 on both sides ✔

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3. NaCl + AgC₂H₃O₂ → NaC₂H₃O₂ + AgCl

Already balanced? Let’s check:

Left: Na=1, Cl=1, Ag=1, C=2, H=3, O=2
Right: Na=1, C=2, H=3, O=2, Ag=1, Cl=1 ✔

→ NaCl + AgC₂H₃O₂ → NaC₂H₃O₂ + AgCl

(All coefficients = 1)

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4. Mg(OH)₂ + H₃PO₄ → H₂O + Mg₃(PO₄)₂

Right has Mg₃ → need 3 Mg(OH)₂ on left
Right has PO₄×2 → need 2 H₃PO₄ on left

Now left: Mg=3, O from OH=6, H from OH=6; plus H₃PO₄×2 → H=6, P=2, O=8 → total H=12, O=14

Right: Mg₃(PO₄)₂ → Mg=3, P=2, O=8
Plus H₂O → need 6 H₂O to get H=12 and O=6 → total O=8+6=14 ✔

→ 3Mg(OH)₂ + 2H₃PO₄ → 6H₂O + Mg₃(PO₄)₂

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5. HNO₃ + Ni → Ni(NO₃)₂ + H₂

Right: Ni=1, N=2, O=6, H=2
Left: H=1, N=1, O=3 per HNO₃ → need 2 HNO₃ for N=2 → but then H=2 → good

But Ni(NO₃)₂ needs 2 NO₃ → so 2 HNO₃ gives 2H and 2NO₃ → perfect

Wait — H₂ gas needs 2H → yes, 2HNO₃ gives 2H → forms H₂

→ 2HNO₃ + Ni → Ni(NO₃)₂ + H₂

Check: Left: H=2, N=2, O=6, Ni=1
Right: Ni=1, N=2, O=6, H=2 ✔

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6. Ba(HCO₃)₂ → BaCO₃ + H₂O + CO₂

Left: Ba=1, H=2, C=2, O=6
Right: Ba=1, C=1 (from BaCO₃) + 1 (from CO₂) = 2, H=2, O=3 (BaCO₃) + 1 (H₂O) + 2 (CO₂) = 6 ✔

→ Ba(HCO₃)₂ → BaCO₃ + H₂O + CO₂

(All coefficients = 1)

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7. BaCl₂ + Na₂SO₄ → NaCl + BaSO₄

Left: Ba=1, Cl=2, Na=2, S=1, O=4
Right: Na=1, Cl=1, Ba=1, S=1, O=4 → not balanced

Need 2 NaCl on right → then Na=2, Cl=2

→ BaCl₂ + Na₂SO₄ → 2NaCl + BaSO₄

✔

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8. Al₂(CO₃)₃ → Al₂O₃ + CO₂

Left: Al=2, C=3, O=9
Right: Al=2, O=3 + ? from CO₂ → need 3 CO₂ to get C=3 and O=6 → total O=3+6=9 ✔

→ Al₂(CO₃)₃ → Al₂O₃ + 3CO₂

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9. Ca + H₂O → Ca(OH)₂ + H₂

Left: Ca=1, H=2, O=1
Right: Ca=1, O=2, H=2 (from OH) + 2 (from H₂) = 4 → too many H

Need 2 H₂O on left → H=4, O=2
Then right: Ca(OH)₂ has O=2, H=2 → plus H₂ has H=2 → total H=4 ✔

→ Ca + 2H₂O → Ca(OH)₂ + H₂

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10. LiHCO₃ → Li₂CO₃ + H₂O + CO₂

Left: Li=1, H=1, C=1, O=3
Right: Li=2 → need 2 LiHCO₃ on left → then Li=2, H=2, C=2, O=6

Right: Li₂CO₃ → Li=2, C=1, O=3
Plus H₂O → H=2, O=1
Plus CO₂ → C=1, O=2 → total C=2, O=6, H=2 ✔

→ 2LiHCO₃ → Li₂CO₃ + H₂O + CO₂

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11. N₂ + O₂ → N₂O₅

Left: N=2, O=2
Right: N=2, O=5 → need 5/2 O₂ → multiply all by 2

→ 2N₂ + 5O₂ → 2N₂O₅

Check: N=4, O=10 on both sides ✔

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12. MgBr₂ + KOH → KBr + Mg(OH)₂

Left: Mg=1, Br=2, K=1, O=1, H=1
Right: K=1, Br=1, Mg=1, O=2, H=2 → not balanced

Need 2 KOH on left → K=2, O=2, H=2
Then need 2 KBr on right → K=2, Br=2

→ MgBr₂ + 2KOH → 2KBr + Mg(OH)₂

✔

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13. Mn + CuCl → Cu + MnCl₂

Left: Mn=1, Cu=1, Cl=1
Right: Cu=1, Mn=1, Cl=2 → not balanced

Need 2 CuCl on left → Cl=2, Cu=2
Then need 2 Cu on right

→ Mn + 2CuCl → 2Cu + MnCl₂

✔

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14. Zn + S₈ → ZnS

Left: Zn=1, S=8
Right: Zn=1, S=1 → need 8 ZnS on right → then Zn=8

So put 8 Zn on left

→ 8Zn + S₈ → 8ZnS

✔

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15. NaOH + H₂SO₄ → H₂O + Na₂SO₄

Left: Na=1, O=1+4=5, H=1+2=3, S=1
Right: Na=2, S=1, O=4 + ? from H₂O → need 2 NaOH on left → Na=2, O=2, H=2 → plus H₂SO₄ → H=2, S=1, O=4 → total H=4, O=6

Right: Na₂SO₄ → Na=2, S=1, O=4
Plus 2 H₂O → H=4, O=2 → total O=6 ✔

→ 2NaOH + H₂SO₄ → 2H₂O + Na₂SO₄

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16. K + H₂O → KOH + H₂

Left: K=1, H=2, O=1
Right: K=1, O=1, H=1 (KOH) + 2 (H₂) = 3 → too many H

Need 2 K on left → then 2 KOH on right → H from KOH=2, plus H₂=2 → total H=4 → need 2 H₂O on left → H=4, O=2

→ 2K + 2H₂O → 2KOH + H₂

Check: Left: K=2, H=4, O=2
Right: K=2, O=2, H=2 (from 2KOH) + 2 (from H₂) = 4 ✔

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17. C₅H₁₂ + O₂ → H₂O + CO₂

Combustion reaction.

Left: C=5, H=12, O=?
Right: Need 5 CO₂ for C=5 → O=10
Need 6 H₂O for H=12 → O=6 → total O=16 → so O₂ needed = 8

→ C₅H₁₂ + 8O₂ → 6H₂O + 5CO₂

Check: C=5, H=12, O=16 on both sides ✔

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18. KOH + H₂CO₃ → H₂O + K₂CO₃

Left: K=1, O=1+3=4, H=1+2=3, C=1
Right: K=2 → need 2 KOH on left → K=2, O=2, H=2 → plus H₂CO₃ → H=2, C=1, O=3 → total H=4, O=5

Right: K₂CO₃ → K=2, C=1, O=3
Plus 2 H₂O → H=4, O=2 → total O=5 ✔

→ 2KOH + H₂CO₃ → 2H₂O + K₂CO₃

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19. C₄H₈O₂ + O₂ → H₂O + CO₂

Combustion.

Left: C=4, H=8, O=2 + ?
Right: 4 CO₂ → C=4, O=8
4 H₂O → H=8, O=4 → total O=12 → minus 2 from fuel → need 10 from O₂ → so 5 O₂

→ C₄H₈O₂ + 5O₂ → 4H₂O + 4CO₂

Check: C=4, H=8, O=2+10=12 → right: O=4+8=12 ✔

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20. Al + S₈ → Al₂S₃

Left: Al=1, S=8
Right: Al=2, S=3 → LCM of S: 24 → so 3 S₈ → S=24 → then Al₂S₃ × 8 → Al=16, S=24

So 16 Al on left

→ 16Al + 3S₈ → 8Al₂S₃

Check: Al=16, S=24 on both sides ✔

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Now, for “Types of Reaction” — the 5 main types are:

1. Synthesis (combination) – A + B → AB
2. Decomposition – AB → A + B
3. Single Replacement – A + BC → AC + B
4. Double Replacement – AB + CD → AD + CB
5. Combustion – hydrocarbon + O₂ → CO₂ + H₂O

Let’s classify each:

1. Zn + 2AgNO₃ → Zn(NO₃)₂ + 2Ag → Single Replacement (Zn replaces Ag)
2. N₂ + 3H₂ → 2NH₃ → Synthesis
3. NaCl + AgC₂H₃O₂ → NaC₂H₃O₂ + AgCl → Double Replacement
4. 3Mg(OH)₂ + 2H₃PO₄ → 6H₂O + Mg₃(PO₄)₂ → Double Replacement (acid-base neutralization)
5. 2HNO₃ + Ni → Ni(NO₃)₂ + H₂ → Single Replacement
6. Ba(HCO₃)₂ → BaCO₃ + H₂O + CO₂ → Decomposition
7. BaCl₂ + Na₂SO₄ → 2NaCl + BaSO₄ → Double Replacement
8. Al₂(CO₃)₃ → Al₂O₃ + 3CO₂ → Decomposition
9. Ca + 2H₂O → Ca(OH)₂ + H₂ → Single Replacement
10. 2LiHCO₃ → Li₂CO₃ + H₂O + CO₂ → Decomposition
11. 2N₂ + 5O₂ → 2N₂O₅ → Synthesis
12. MgBr₂ + 2KOH → 2KBr + Mg(OH)₂ → Double Replacement
13. Mn + 2CuCl → 2Cu + MnCl₂ → Single Replacement
14. 8Zn + S₈ → 8ZnS → Synthesis
15. 2NaOH + H₂SO₄ → 2H₂O + Na₂SO₄ → Double Replacement (neutralization)
16. 2K + 2H₂O → 2KOH + H₂ → Single Replacement
17. C₅H₁₂ + 8O₂ → 6H₂O + 5CO₂ → Combustion
18. 2KOH + H₂CO₃ → 2H₂O + K₂CO₃ → Double Replacement (neutralization)
19. C₄H₈O₂ + 5O₂ → 4H₂O + 4CO₂ → Combustion
20. 16Al + 3S₈ → 8Al₂S₃ → Synthesis

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Final Answer:

Balanced Equations:

1. Zn + 2AgNO₃ → Zn(NO₃)₂ + 2Ag
2. N₂ + 3H₂ → 2NH₃
3. NaCl + AgC₂H₃O₂ → NaC₂H₃O₂ + AgCl
4. 3Mg(OH)₂ + 2H₃PO₄ → 6H₂O + Mg₃(PO₄)₂
5. 2HNO₃ + Ni → Ni(NO₃)₂ + H₂
6. Ba(HCO₃)₂ → BaCO₃ + H₂O + CO₂
7. BaCl₂ + Na₂SO₄ → 2NaCl + BaSO₄
8. Al₂(CO₃)₃ → Al₂O₃ + 3CO₂
9. Ca + 2H₂O → Ca(OH)₂ + H₂
10. 2LiHCO₃ → Li₂CO₃ + H₂O + CO₂
11. 2N₂ + 5O₂ → 2N₂O₅
12. MgBr₂ + 2KOH → 2KBr + Mg(OH)₂
13. Mn + 2CuCl → 2Cu + MnCl₂
14. 8Zn + S₈ → 8ZnS
15. 2NaOH + H₂SO₄ → 2H₂O + Na₂SO₄
16. 2K + 2H₂O → 2KOH + H₂
17. C₅H₁₂ + 8O₂ → 6H₂O + 5CO₂
18. 2KOH + H₂CO₃ → 2H₂O + K₂CO₃
19. C₄H₈O₂ + 5O₂ → 4H₂O + 4CO₂
20. 16Al + 3S₈ → 8Al₂S₃

Reaction Types:

1. Single Replacement
2. Synthesis
3. Double Replacement
4. Double Replacement
5. Single Replacement
6. Decomposition
7. Double Replacement
8. Decomposition
9. Single Replacement
10. Decomposition
11. Synthesis
12. Double Replacement
13. Single Replacement
14. Synthesis
15. Double Replacement
16. Single Replacement
17. Combustion
18. Double Replacement
19. Combustion
20. Synthesis