Science • Prep 3 (Grade 9)
Estimated Time: 35 mins
Unit 1 - Lesson 1: Types of Chemical Reactions
Explore fundamental chemical reactions: thermal decomposition, the Chemical Activity Series, single and double substitution reactions, and redox processes.
1. Thermal Decomposition Reactions
Definition:
Chemical reactions where compounds are broken down by heat into simpler substances or their primary elements.
| Compound Type | Balanced Equation | Observation & Color Change |
|---|---|---|
| 1. Metal Oxides | 2HgO --(Δ)--> 2Hg + O2↑ | Red mercuric oxide decomposes into silver mercury and oxygen gas (relights a glowing splint). |
| 2. Metal Hydroxides | Cu(OH)2 --(Δ)--> CuO + H2O↑ | Blue copper hydroxide decomposes into black copper oxide and water vapor. |
| 3. Metal Carbonates | CuCO3 --(Δ)--> CuO + CO2↑ | Green copper carbonate decomposes into black copper oxide and CO2 (turbid limewater). |
| 4. Metal Sulfates | CuSO4 --(Δ)--> CuO + SO3↑ | Blue copper sulfate decomposes into black copper oxide and sulfur trioxide gas. |
| 5. Metal Nitrates | 2NaNO3 --(Δ)--> 2NaNO2 + O2↑ | White sodium nitrate decomposes into yellowish-white sodium nitrite and oxygen gas. |
2. Chemical Activity Series (CAS) & Substitution
Chemical Activity Series:
The arrangement of metals in descending order according to their chemical activity:
K > Na > Ca > Mg > Al > Zn > Fe > Sn > Pb > [H] > Cu > Hg > Ag > Pt > Au
Single Substitution Reactions
A more active metal replaces a less active metal or hydrogen.
- Zinc replaces hydrogen of acid:
Zn + 2HCl --> ZnCl2 + H2↑ - Magnesium replaces copper:
Mg + CuSO4 --> MgSO4 + Cu↓ (red ppt)
Double Substitution Reactions
Mutual exchange of ions between two compounds.
- Neutralization (Acid + Base → Salt + Water):
NaOH + HCl --> NaCl + H2O - Precipitation:
NaCl + AgNO3 --> NaNO3 + AgCl↓ (white ppt of silver chloride)
3. Interactive Assessment Quiz
Choose the correct answer for each question, then click "Submit Answers":
التعليقات والمناقشة