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SSC CHSL 2027 Common Chemistry Reactions: Important Equations and Examples
4/11/2026
SSC CHSL 2027 Common Chemistry Reactions: Important Equations and Examples
Chemical reactions are an important topic in General Science for SSC CHSL 2027. Questions may be based on reaction types, chemical equations, oxidation, reduction, acids, bases and common chemical changes observed in everyday life.
This quick revision guide covers important chemical reactions, balanced equations, simple explanations and practice MCQs to help you prepare for the examination.
1. Important Types of Chemical Reactions
| Reaction Type | Meaning | Example |
|---|---|---|
| Combination | Two or more substances form one product. | 2H₂ + O₂ → 2H₂O |
| Decomposition | One compound breaks into simpler substances. | CaCO₃ → CaO + CO₂ |
| Displacement | A more reactive element replaces a less reactive element. | Zn + CuSO₄ → ZnSO₄ + Cu |
| Double Displacement | Two compounds exchange ions. | Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl |
| Neutralisation | An acid reacts with a base to form salt and water. | HCl + NaOH → NaCl + H₂O |
| Combustion | A substance reacts with oxygen, usually releasing heat. | CH₄ + 2O₂ → CO₂ + 2H₂O |
2. Common Chemical Reactions and Their Equations
1. Burning of Magnesium: Magnesium burns in oxygen with a bright white flame and forms magnesium oxide.
2Mg + O₂ → 2MgO
2. Formation of Water: Hydrogen combines with oxygen to form water.
2H₂ + O₂ → 2H₂O
3. Thermal Decomposition of Limestone: Calcium carbonate breaks down on heating to form calcium oxide and carbon dioxide.
CaCO₃ → CaO + CO₂
4. Iron and Copper Sulphate: Iron displaces copper from copper sulphate solution. The blue solution changes to pale green.
Fe + CuSO₄ → FeSO₄ + Cu
5. Formation of Silver Chloride: Silver nitrate reacts with sodium chloride to form a white precipitate of silver chloride.
AgNO₃ + NaCl → AgCl ↓ + NaNO₃
6. Reaction of Zinc with Hydrochloric Acid: Zinc reacts with dilute hydrochloric acid and releases hydrogen gas.
Zn + 2HCl → ZnCl₂ + H₂ ↑
3. Oxidation and Reduction Reactions
- Oxidation: Addition of oxygen, removal of hydrogen or loss of electrons.
- Reduction: Removal of oxygen, addition of hydrogen or gain of electrons.
- Redox Reaction: A reaction in which oxidation and reduction occur simultaneously.
Important Example:
CuO + H₂ → Cu + H₂O
In this reaction, copper oxide loses oxygen and is reduced to copper. Hydrogen gains oxygen and is oxidised to water.
4. Chemical Reactions in Everyday Life
| Everyday Process | Chemical Explanation |
|---|---|
| Rusting of Iron | Iron reacts with oxygen and moisture to form hydrated iron oxide (rust). |
| Curd Formation | Bacteria convert lactose into lactic acid. |
| Digestion | Complex food molecules are broken into simpler substances through chemical processes. |
| Respiration | Glucose reacts with oxygen and releases energy. |
| Rancidity | Oxidation of fats and oils causes unpleasant smell and taste. |
| Whitewashing | Calcium hydroxide reacts with carbon dioxide to form calcium carbonate. |
Whitewashing Reaction:
Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
5. Important Chemistry Facts for Quick Revision
- Rust is mainly hydrated iron(III) oxide.
- Quicklime is calcium oxide (CaO).
- Slaked lime is calcium hydroxide [Ca(OH)₂].
- Washing soda is sodium carbonate decahydrate (Na₂CO₃·10H₂O).
- Baking soda is sodium hydrogen carbonate (NaHCO₃).
- Common salt is sodium chloride (NaCl).
- Vinegar contains acetic acid.
- Lemon juice contains citric acid.
- Plaster of Paris is calcium sulphate hemihydrate (CaSO₄·½H₂O).
6. SSC CHSL 2027 Common Chemistry Reactions Practice Questions
Choose the correct option for each question.
Q1. Which gas is released when zinc reacts with dilute hydrochloric acid?
A. Oxygen
B. Nitrogen
C. Hydrogen
D. Carbon dioxide
Q2. Which reaction is an example of thermal decomposition?
A. 2H₂ + O₂ → 2H₂O
B. CaCO₃ → CaO + CO₂
C. Zn + CuSO₄ → ZnSO₄ + Cu
D. HCl + NaOH → NaCl + H₂O
Q3. What is formed when magnesium burns in oxygen?
A. Magnesium chloride
B. Magnesium oxide
C. Magnesium sulphate
D. Magnesium carbonate
Q4. Which type of reaction occurs when iron is placed in copper sulphate solution?
A. Combination
B. Decomposition
C. Displacement
D. Neutralisation
Q5. Which gas turns limewater milky?
A. Oxygen
B. Hydrogen
C. Nitrogen
D. Carbon dioxide
Q6. Which substance is formed during the whitewashing reaction that gives walls a shiny finish?
A. Calcium carbonate
B. Calcium chloride
C. Sodium carbonate
D. Calcium sulphate
Q7. Which of the following is a neutralisation reaction?
A. Zn + 2HCl → ZnCl₂ + H₂
B. HCl + NaOH → NaCl + H₂O
C. CaCO₃ → CaO + CO₂
D. 2Mg + O₂ → 2MgO
Q8. What is the chemical formula of baking soda?
A. Na₂CO₃
B. NaCl
C. NaHCO₃
D. CaCO₃
Q9. Which process involves oxidation of fats and oils?
A. Neutralisation
B. Rancidity
C. Crystallisation
D. Sublimation
Q10. In the reaction CuO + H₂ → Cu + H₂O, which substance is reduced?
A. Hydrogen
B. Water
C. Copper oxide
D. Oxygen
Answer Key with Explanations
| Q. | Answer | Explanation |
|---|---|---|
| 1 | C. Hydrogen | Zinc reacts with dilute HCl and releases hydrogen gas. |
| 2 | B. CaCO₃ → CaO + CO₂ | Calcium carbonate decomposes on heating. |
| 3 | B. Magnesium oxide | Magnesium combines with oxygen to form MgO. |
| 4 | C. Displacement | Iron displaces copper because it is more reactive. |
| 5 | D. Carbon dioxide | CO₂ reacts with limewater to form insoluble calcium carbonate. |
| 6 | A. Calcium carbonate | It forms when slaked lime reacts with atmospheric CO₂. |
| 7 | B. HCl + NaOH → NaCl + H₂O | An acid and a base form salt and water. |
| 8 | C. NaHCO₃ | NaHCO₃ is sodium hydrogen carbonate or baking soda. |
| 9 | B. Rancidity | Oxidation of fats and oils causes rancidity. |
| 10 | C. Copper oxide | CuO loses oxygen and changes into copper. |
7. Preparation Tips for SSC CHSL 2027
- Memorise common reaction types with one balanced equation each.
- Practise identifying reactants and products.
- Revise oxidation and reduction using oxygen gain and loss.
- Learn common chemical names and their formulas.
- Understand everyday examples such as rusting, rancidity and whitewashing.
- Practise reaction-identification MCQs regularly.
Prepare for SSC CHSL 2027 with Katara Academy
Common chemical reactions become easier to remember when you connect equations with their reaction types and everyday applications. Revise the important equations and practise General Science questions regularly.
Explore General Science and exam preparation courses at Katara Academy.
Frequently Asked Questions (FAQs)
1. What are the main types of chemical reactions?
Common types include combination, decomposition, displacement, double displacement, combustion and neutralisation reactions. Oxidation-reduction is another important classification.
2. Which gas is released when zinc reacts with hydrochloric acid?
Hydrogen gas is released when zinc reacts with dilute hydrochloric acid.
3. What causes rusting of iron?
Rusting occurs when iron reacts with oxygen in the presence of moisture, forming hydrated iron oxide.
4. What is the difference between oxidation and reduction?
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