Classification of chemical reactions CHM 02 worksheet 2 | PDF - Free Printable

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

We’re looking for:
- Synthesis: Two or more substances combine to form one product. (A + B → AB)
- Decomposition: One compound 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 substance reacts with oxygen, often producing CO₂ and H₂O — usually involves O₂ as a reactant and releases energy.

Note: Some reactions can be more than one type — especially combustion is also often synthesis if it forms one product from elements.

---

1. 2H₂ + O₂ → 2H₂O

→ Hydrogen and oxygen combine to make water. That’s synthesis.
→ Also, it’s reacting with oxygen and releasing energy — so it’s combustion too.
✔ Synthesis and Combustion

---

2. 2H₂O --(electricity)--> 2H₂ + O₂

→ Water breaks down into hydrogen and oxygen gas using electricity.
→ One compound breaking into elements = decomposition.
✔ Decomposition

---

3. Zn + H₂SO₄ → ZnSO₄ + H₂

→ Zinc replaces hydrogen in sulfuric acid.
→ Element + compound → new compound + different element.
✔ Single Replacement

---

4. 2CO + O₂ → 2CO₂

→ Carbon monoxide reacts with oxygen to make carbon dioxide.
→ Reacts with O₂ → likely combustion.
→ Also, two things combining? But CO is already a compound — not pure elements forming one product → NOT synthesis.
Wait — combustion doesn’t have to start with elements. Burning CO is a classic combustion reaction.
✔ Combustion

*(Note: Not synthesis because CO is not an element — synthesis typically starts with elements.)*

---

5. 2HgO --(heat)--> 2Hg + O₂

→ Mercury(II) oxide breaks down into mercury metal and oxygen gas when heated.
→ One compound → two simpler substances.
✔ Decomposition

---

6. 2KBr + Cl₂ → 2KCl + Br₂

→ Chlorine replaces bromine in potassium bromide.
→ Element + compound → new compound + different element.
✔ Single Replacement

---

7. CaO + H₂O → Ca(OH)₂

→ Calcium oxide and water combine to make calcium hydroxide.
→ Two substances → one product.
✔ Synthesis

---

8. AgNO₃ + NaCl → AgCl + NaNO₃

→ Silver nitrate and sodium chloride swap partners: silver pairs with chloride, sodium with nitrate.
→ Classic double replacement (also called metathesis).
✔ Double Replacement

---

9. 2H₂O₂ --(heat)--> 2H₂O + O₂

→ Hydrogen peroxide breaks down into water and oxygen gas when heated.
→ One compound → two products.
✔ Decomposition

---

10. Cu(OH)₂ + H₂SO₄ → CuSO₄ + 2H₂O

→ Copper(II) hydroxide and sulfuric acid react.
→ This looks like an acid-base neutralization — which is a type of double replacement.
→ OH⁻ from base and H⁺ from acid form water; Cu²⁺ and SO₄²⁻ form salt.
✔ Double Replacement

*(Also could be called neutralization, but since that’s not listed, double replacement is correct.)*

---

Final Answer:

1. Synthesis and Combustion
2. Decomposition
3. Single Replacement
4. Combustion
5. Decomposition
6. Single Replacement
7. Synthesis
8. Double Replacement
9. Decomposition
10. Double Replacement