Types of Chemical Reactions — Answer Key
Signs of a chemical reaction: change of color • bubbles / gas released • fire or temperature change • formation of a precipitate
Do Now — Words to Formula
1. Lithium hydroxide (LiOH) + sulfuric acid (H₂SO₄) → lithium sulfate + water
2LiOH + H₂SO₄ → Li₂SO₄ + 2H₂O
Balance check: Li 2=2, O 2+4=4+2 ✓ H 2+2=4 ✓ S 1=1 ✓
Double Replacement (Neutralization)
2. Calcium carbonate (CaCO₃) + hydrochloric acid (HCl) → calcium chloride + water + carbon dioxide gas
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
Balance check: Ca 1=1, C 1=1, O 3=1+2 ✓ Cl 2=2 ✓ H 2=2 ✓
Double Replacement
Part A — Words to Formula
1. Magnesium metal burns in oxygen gas to produce magnesium oxide (MgO).
2Mg + O₂ → 2MgO
Balance: Mg 2=2, O 2=2 ✓
Synthesis (Combination)
2. Water (H₂O) is broken down by electrolysis into hydrogen gas and oxygen gas.
2H₂O → 2H₂ + O₂
Balance: H 4=4, O 2=2 ✓
Decomposition
3. Iron (Fe) reacts with copper(II) sulfate solution (CuSO₄) to produce iron(II) sulfate (FeSO₄) and copper metal.
Fe + CuSO₄ → FeSO₄ + Cu
Already balanced. Fe and Cu each swap once. ✓
Single Replacement
4. Sodium hydroxide (NaOH) reacts with hydrochloric acid (HCl) to produce sodium chloride and water.
NaOH + HCl → NaCl + H₂O
Already balanced. ✓
Double Replacement (Neutralization)
5. Propane gas (C₃H₈) undergoes complete combustion in oxygen. (Products: CO₂ and H₂O)
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
Balance C first: 3. Then H: 8 H → 4 H₂O. Then O: products = 6+4 = 10 O → 5 O₂ ✓
Combustion
Part B — Identify & Balance
1. Fe + O₂ → Fe₂O₃
4Fe + 3O₂ → 2Fe₂O₃
Fe: 4=4, O: 6=6 ✓
Synthesis
2. H₂O₂ → H₂O + O₂
2H₂O₂ → 2H₂O + O₂
H: 4=4, O: 4=2+2 ✓
Decomposition
3. Al + CuSO₄ → Al₂(SO₄)₃ + Cu
2Al + 3CuSO₄ → Al₂(SO₄)₃ + 3Cu
Al: 2=2, Cu: 3=3, SO₄: 3=3 ✓
Single Replacement
4. KOH + H₂SO₄ → K₂SO₄ + H₂O
2KOH + H₂SO₄ → K₂SO₄ + 2H₂O
K: 2=2, O: 2+4=4+2=6 ✓ H: 2+2=4 ✓ S: 1=1 ✓
Double Replacement (Acid-Base)
5. C₄H₁₀ + O₂ → CO₂ + H₂O (butane)
2C₄H₁₀ + 13O₂ → 8CO₂ + 10H₂O
Balance C first: 4 → 4CO₂. H: 10 → 5H₂O. O: 8+5=13 → 13/2 O₂ → multiply all ×2. C: 8=8, H: 20=20, O: 26=16+10=26 ✓
Combustion
Answer key — for instructor reference