Classification of Reactions worksheet - Free Printable

Let’s go through each reaction one by one and classify it based on the type of chemical reaction.

We have 5 types to choose from:
- Synthesis: Two or more substances combine to form ONE product. (A + B → AB)
- Decomposition: ONE substance breaks down into two or more simpler substances. (AB → A + B)
- Single Replacement: One element replaces another in a compound. (A + BC → AC + B)
- Double Replacement: Ions swap between two compounds. (AB + CD → AD + CB)
- Combustion: A hydrocarbon (or sometimes other fuel) reacts with oxygen to produce CO₂ and H₂O. Often releases heat/light.

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1. 2H₂ + O₂ → 2H₂O
Two elements combining to make one compound → Synthesis

2. 2H₂O → 2H₂ + O₂
One compound breaking into two elements → Decomposition

3. CH₄ + O₂ → CO₂ + H₂O
Hydrocarbon + oxygen → carbon dioxide + water → Combustion

4. Zn + H₂SO₄ → ZnSO₄ + H₂
Zinc replaces hydrogen in sulfuric acid → Single Replacement

5. HgO → Hg + O₂
One compound breaks into two elements → Decomposition

6. C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
Sugar reacting with oxygen to make CO₂ and water → This is cellular respiration, but still classified as Combustion (same pattern)

7. CO + O₂ → CO₂
Carbon monoxide + oxygen → carbon dioxide → This is also a combustion-like reaction (burning CO), so Combustion

Wait — actually, let’s double-check: Is this really combustion? Combustion usually involves a fuel burning in oxygen to release energy. CO can burn to form CO₂, so yes — Combustion

But some might argue it’s synthesis too (two things making one). However, since it involves oxygen and produces an oxide with energy release, we’ll stick with Combustion.

Actually — hold on! Let’s be precise. The classic definition of combustion requires a hydrocarbon or organic compound. But technically, any reaction where a substance combines rapidly with oxygen releasing heat/light is combustion. CO burning fits that. So Combustion is acceptable.

Alternatively, if your teacher says only hydrocarbons count, then maybe not. But looking at problem #6 (glucose) being combustion, and glucose isn’t a hydrocarbon either — it has oxygen — so probably they’re using “combustion” broadly for reactions with O₂ producing oxides.

So yes — Combustion

8. KBr + Cl₂ → KCl + Br₂
Chlorine replaces bromine in potassium bromide → Single Replacement

9. CaO + H₂O → Ca(OH)₂
Two compounds combine to make one → Synthesis

10. AgNO₃ + NaCl → AgCl + NaNO₃
Ions swap: silver pairs with chloride, sodium with nitrate → Double Replacement

11. H₂O₂ → H₂O + O₂
One compound breaks into two → Decomposition

12. Ca(OH)₂ + H₂SO₄ → CaSO₄ + 2H₂O
Acid-base neutralization — ions swap → Double Replacement

13. N₂O₄ → 2NO₂
One compound breaks into two molecules (still same elements, but different arrangement) → Still counts as Decomposition

14. Fe + O₂ → FeO
Iron + oxygen → iron oxide → Combination of elements → Synthesis

(Note: It should be balanced as 2Fe + O₂ → 2FeO, but classification doesn’t depend on balancing.)

15. Al + Cl₂ → AlCl₃
Aluminum + chlorine → aluminum chloride → Two elements forming one compound → Synthesis

16. BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl
Ions swap: barium with sulfate, sodium with chloride → Double Replacement

17. Mg + CuSO₄ → Cu + MgSO₄
Magnesium replaces copper → Single Replacement

18. CaO + SiO₂ → CaSiO₃
Two compounds combine to make one → Synthesis

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Now, Part 2 asks to balance equations in problems: 3, 5, 7, 8, 11, 14, 15.

Let’s do those now.

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Problem 3: CH₄ + O₂ → CO₂ + H₂O

Left: C=1, H=4, O=2
Right: C=1, H=2, O=3

Balance H first: put 2 in front of H₂O → now H=4 on right

CH₄ + O₂ → CO₂ + 2H₂O

Now O: right has 2 (from CO₂) + 2 (from 2H₂O) = 4 oxygens → need 2 O₂ on left

✔ Balanced: CH₄ + 2O₂ → CO₂ + 2H₂O

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Problem 5: HgO → Hg + O₂

Left: Hg=1, O=1
Right: Hg=1, O=2

Need 2 HgO on left to get even oxygen:

2HgO → ? Hg + O₂

Now Hg: 2 on left → need 2 Hg on right

✔ Balanced: 2HgO → 2Hg + O₂

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Problem 7: CO + O₂ → CO₂

Left: C=1, O=1+2=3
Right: C=1, O=2

Try putting 2 CO and 2 CO₂:

2CO + O₂ → 2CO₂

Check: Left: C=2, O=2+2=4; Right: C=2, O=4 → ✔

Balanced: 2CO + O₂ → 2CO₂

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Problem 8: KBr + Cl₂ → KCl + Br₂

Left: K=1, Br=1, Cl=2
Right: K=1, Cl=1, Br=2

Need 2 KBr and 2 KCl:

2KBr + Cl₂ → 2KCl + Br₂

Check: K=2, Br=2, Cl=2 on both sides → ✔

Balanced: 2KBr + Cl₂ → 2KCl + Br₂

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Problem 11: H₂O₂ → H₂O + O₂

Left: H=2, O=2
Right: H=2, O=1+2=3 → not balanced

Try 2 H₂O₂ → ?

2H₂O₂ → 2H₂O + O₂

Left: H=4, O=4
Right: H=4, O=2+2=4 → ✔

Balanced: 2H₂O₂ → 2H₂O + O₂

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Problem 14: Fe + O₂ → FeO

Left: Fe=1, O=2
Right: Fe=1, O=1

Need 2 FeO on right → then need 2 Fe on left

2Fe + O₂ → 2FeO

Check: Fe=2, O=2 on both → ✔

Balanced: 2Fe + O₂ → 2FeO

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Problem 15: Al + Cl₂ → AlCl₃

Left: Al=1, Cl=2
Right: Al=1, Cl=3

Find LCM of 2 and 3 → 6

So 3 Cl₂ (gives 6 Cl) and 2 AlCl₃ (needs 6 Cl and 2 Al)

Then need 2 Al on left

✔ Balanced: 2Al + 3Cl₂ → 2AlCl₃

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Final Answers:

Part 1 Classifications:

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

Part 2 Balanced Equations:

3. CH₄ + 2O₂ → CO₂ + 2H₂O
5. 2HgO → 2Hg + O₂
7. 2CO + O₂ → 2CO₂
8. 2KBr + Cl₂ → 2KCl + Br₂
11. 2H₂O₂ → 2H₂O + O₂
14. 2Fe + O₂ → 2FeO
15. 2Al + 3Cl₂ → 2AlCl₃

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

Part 2:
3. CH₄ + 2O₂ → CO₂ + 2H₂O
5. 2HgO → 2Hg + O₂
7. 2CO + O₂ → 2CO₂
8. 2KBr + Cl₂ → 2KCl + Br₂
11. 2H₂O₂ → 2H₂O + O₂
14. 2Fe + O₂ → 2FeO
15. 2Al + 3Cl₂ → 2AlCl₃