Worksheet #3 with Key on Decomposition Reactions | Exercises ... - Free Printable

Let's solve each decomposition reaction step by step. In decomposition reactions, a single compound breaks down into two or more simpler substances. These reactions often require energy (like heat) to proceed.

We’ll write the balanced chemical equations for each compound decomposing, based on common decomposition patterns:

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1. Barium carbonate →

Barium carbonate decomposes into barium oxide and carbon dioxide.
$$
\text{BaCO}_3 \rightarrow \text{BaO} + \text{CO}_2
$$

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2. Magnesium carbonate →

Magnesium carbonate decomposes into magnesium oxide and carbon dioxide.
$$
\text{MgCO}_3 \rightarrow \text{MgO} + \text{CO}_2
$$

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3. Potassium carbonate →

Potassium carbonate is stable and does not readily decompose under normal conditions, but upon strong heating, it can decompose into potassium oxide and carbon dioxide.
$$
\text{K}_2\text{CO}_3 \rightarrow \text{K}_2\text{O} + \text{CO}_2
$$

> Note: This is less common than other carbonates due to potassium’s stability.

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4. Zinc hydroxide →

Zinc hydroxide decomposes into zinc oxide and water.
$$
\text{Zn(OH)}_2 \rightarrow \text{ZnO} + \text{H}_2\text{O}
$$

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5. Iron(II) hydroxide →

Iron(II) hydroxide decomposes into iron(II) oxide and water.
$$
\text{Fe(OH)}_2 \rightarrow \text{FeO} + \text{H}_2\text{O}
$$

> Note: FeO may oxidize further in air, but this is the primary decomposition product.

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6. Nickel(II) chlorate →

Chlorates decompose when heated to produce metal chloride and oxygen gas.
$$
2\text{Ni(ClO}_3)_2 \rightarrow 2\text{NiCl}_2 + 3\text{O}_2
$$

> General pattern: $ 2\text{M(ClO}_3)_2 \rightarrow 2\text{MCl}_2 + 3\text{O}_2 $

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7. Sodium chlorate →

Sodium chlorate decomposes into sodium chloride and oxygen.
$$
2\text{NaClO}_3 \rightarrow 2\text{NaCl} + 3\text{O}_2
$$

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8. Potassium chlorate →

Same as above — decomposes to potassium chloride and oxygen.
$$
2\text{KClO}_3 \rightarrow 2\text{KCl} + 3\text{O}_2
$$

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9. Sulfuric acid →

Sulfuric acid decomposes upon strong heating to form sulfur trioxide and water.
$$
\text{H}_2\text{SO}_4 \rightarrow \text{SO}_3 + \text{H}_2\text{O}
$$

> Note: SO₃ may further react with water to reform H₂SO₄, but under high heat, this decomposition occurs.

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10. Carbonic acid →

Carbonic acid is unstable and spontaneously decomposes into carbon dioxide and water.
$$
\text{H}_2\text{CO}_3 \rightarrow \text{CO}_2 + \text{H}_2\text{O}
$$

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11. Aluminum oxide →

Aluminum oxide is very stable and does not decompose easily. It requires extreme conditions (electrolysis), so it typically does not undergo simple thermal decomposition.
$$
\text{Al}_2\text{O}_3 \rightarrow \text{No decomposition (stable)}
$$

> However, if forced (e.g., via electrolysis):
> $ 2\text{Al}_2\text{O}_3 \rightarrow 4\text{Al} + 3\text{O}_2 $ — but this is not a typical decomposition reaction.

So, for most purposes:
→ No decomposition (or "does not decompose under normal conditions")

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12. Silver oxide →

Silver oxide decomposes upon heating into silver metal and oxygen gas.
$$
2\text{Ag}_2\text{O} \rightarrow 4\text{Ag} + \text{O}_2
$$

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✔ Final Answers (Balanced Equations):

1. $\text{BaCO}_3 \rightarrow \text{BaO} + \text{CO}_2$
2. $\text{MgCO}_3 \rightarrow \text{MgO} + \text{CO}_2$
3. $\text{K}_2\text{CO}_3 \rightarrow \text{K}_2\text{O} + \text{CO}_2$
4. $\text{Zn(OH)}_2 \rightarrow \text{ZnO} + \text{H}_2\text{O}$
5. $\text{Fe(OH)}_2 \rightarrow \text{FeO} + \text{H}_2\text{O}$
6. $2\text{Ni(ClO}_3)_2 \rightarrow 2\text{NiCl}_2 + 3\text{O}_2$
7. $2\text{NaClO}_3 \rightarrow 2\text{NaCl} + 3\text{O}_2$
8. $2\text{KClO}_3 \rightarrow 2\text{KCl} + 3\text{O}_2$
9. $\text{H}_2\text{SO}_4 \rightarrow \text{SO}_3 + \text{H}_2\text{O}$
10. $\text{H}_2\text{CO}_3 \rightarrow \text{CO}_2 + \text{H}_2\text{O}$
11. $\text{Al}_2\text{O}_3 \rightarrow \text{No decomposition (stable)}$
12. $2\text{Ag}_2\text{O} \rightarrow 4\text{Ag} + \text{O}_2$

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🔍 Summary of Patterns:

- Carbonates: MCO₃ → MO + CO₂ (except some alkali metals)
- Hydroxides: M(OH)₂ → MO + H₂O
- Chlorates: M(ClO₃)₂ → MCl₂ + O₂ (with coefficient balancing)
- Acids: H₂CO₃ → CO₂ + H₂O; H₂SO₄ → SO₃ + H₂O
- Metal oxides: Most are stable; only some (like Ag₂O) decompose to metal + O₂

Let me know if you'd like these written with states (s, l, g) or explained further!