Science Chemistry Reactions
Quick Revision Sheet: Chemistry Reactions (RRB)
“Revise today, recall tomorrow.”
1. Reaction Types – 60-Second Map
| Type | Quick ID | One-Liner Rule | Exam Trap |
|---|---|---|---|
| Combination | A + B → AB | “Marriage” – two become one | Always exothermic |
| Decomposition | AB → A + B | “Divorce” – needs heat/light | Endothermic |
| Displacement | A + BC → AC + B | “Bullying” – more reactive kicks out | Activity series decides |
| Double Displacement | AB + CD → AD + CB | “Partner swap” | Precipitate/gas/water must form |
| Redox | Oxidation = +O/–H; Reduction = –O/+H | OIL RIG | Oxidising agent itself reduced & vice-versa |
2. Must-Know Equations (Write → 3 times)
| Reaction | Balanced Form | Colour/Note |
|---|---|---|
| Rusting | 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃ → Fe₂O₃·xH₂O | Red-brown flaky |
| Photosynthesis | 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ | Chlorophyll, sunlight |
| Saponification | Fat + NaOH → Soap + Glycerol | Exothermic, gives soap |
| Thermite | 2Al + Fe₂O₃ → 2Fe + Al₂O₃ + heat | Railway welding |
3. Redox Shortcuts
- OIL RIG: Oxidation Is Loss (e⁻), Reduction Is Gain (e⁻)
- LEO the lion says GER: Loss Electrons Oxidation, Gain Electrons Reduction
- Oxidising agents: O₂, KMnO₄, K₂Cr₂O₇ (remember “OCK” – Oxidisers Come with K)
- Reducing agents: H₂, C, CO, SO₂ (remember “HCCS” – Help Carbon Cut Stuff)
4. Activity Series (Top 6 only)
K > Na > Ca > Mg > Al > Zn
Mnemonic: Kings Never Carry Many Adorable Zebras
(Any metal can displace the one below it from salt solution.)
5. Precipitate Colours – Flash Table
| Compound | Colour | Memory Hook |
|---|---|---|
| BaSO₄ | White | “Barium Snow” |
| PbI₂ | Bright yellow | “Lead Iodide = Yellow Paint” |
| Cu(OH)₂ | Pale blue | “Copper Sky” |
| Fe(OH)₃ | Red-brown | “Rusty iron” |
6. Common Exam Q&A
Q1: Which gas turns lime-water milky?
CO₂ (Carbon dioxide)Q2: In thermite reaction, which metal acts as reducing agent?
AluminiumQ3: What is the oxidation state of Mn in KMnO₄?
+7Q4: Name the catalyst used in Haber’s process.
Finely divided Iron (Fe)Q5: What type of reaction is: 2H₂O₂ → 2H₂O + O₂?
Decomposition (and also redox)7. 2-Mark Cheat Facts
- Quick balancing trick: Balance “O” last, “H” second-last, metals first.
- Flame colours: Na-yellow, K-lilac, Cu-green, Ca-brick red.
- Acid + Metal → Salt + H₂ (only if metal is above H in activity series).
- All neutralisations are exothermic; ∆H ≈ –57 kJ mol⁻¹ (remember “–57” for MCQ).
8. Last-Night Mnemonics
- “SOAP” – Saponification = Soap + Glycerol
- “O-C-B” – Oxidation-Combination-Burning (all add oxygen).
- “C-B-G” – Copper-Blue-Green (flame & hydroxide colour).
9. 30-Second Self-Test
- Write any one displacement reaction.
- Name the product that makes saponification mixture foam.
- Give the colour of precipitate when Na₂SO₄ + BaCl₂ mix.
(Answers: 1. Zn + CuSO₄ → ZnSO₄ + Cu, 2. Soap, 3. White BaSO₄)
Revise → Sleep → Recall → Rule the exam!
BETA
