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ICSE Class 8 Chemistry Question 3 of 15

Chemical Reactions — Question 6

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Question 6

How will you obtain?

(a) Magnesium oxide from magnesium.

(b) Silver chloride from silver nitrate.

(c) Nitrogen dioxide from lead nitrate.

(d) Zinc chloride from zinc.

(e) Ammonia from nitrogen.

Also give balanced equations for the reactions.

Answer

(a) When magnesium reacts with oxygen it produces magnesium oxide.

2Mg + O2 ⟶ 2MgO

(b) When silver nitrate reacts with hydrochloric acid silver chloride is formed.

AgNO3 (aq) + HCl ⟶ AgCl↓ + HNO3

(c) When lead nitrate is heated strongly, a reddish brown gas nitrogen dioxide is produced.

2Pb(NO3)2 →Δ\xrightarrow{\enspace\Delta\enspace} 2PbO + 4NO2 (g) + O2 (g)

(d) Zinc reacts with dilute HCl to produce zinc chloride.

Zn + 2HCl (dil.) ⟶ ZnCl2 + H2 (g)

(e) When nitrogen gas reacts with hydrogen gas in presence of finely divided iron as catalyst, subjected to pressure of 200-900 atm and temperature of about 450°C, ammonia gas is produced.

     N2+3H2⇌200-900 atmos.Fe catalyst/450°C 2NH3\text{N}_2 + 3\text{H}_2 \xrightleftharpoons[\text{200-900 atmos.}]{\text{Fe catalyst/450\degree C }} \text{2NH}_3

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Chemistry | Chapter 5: Chemical ReactionsWeb Content / Study Guide

Chemical Reactions — Interactive Study Guide

Quick Concept Map

CHANGES: Physical (reversible, no new substance) vs Chemical (irreversible, new substance)
REACTION TYPES: Combination | Decomposition | Displacement | Double Displacement
ENERGY: Exothermic (releases heat) vs Endothermic (absorbs heat)
REDOX: Oxidation (gain O / lose H) + Reduction (lose O / gain H) happening together

Four Types of Reactions — Quick Reference

TypePatternEasy Memory AidExample
CombinationA + B → ABJoining togetherMg + O2 → MgO
DecompositionAB → A + BBreaking apartCaCO3 → CaO + CO2
DisplacementA + BC → AC + BBully kicks out the weakFe + CuSO4 → FeSO4 + Cu
Double DisplacementAB + CD → AD + CBExchange partnersNaCl + AgNO3 → AgCl + NaNO3

Signs of a Chemical Reaction

  1. Change in colour
  2. Evolution of gas (bubbles)
  3. Change in temperature (hot or cold)
  4. Formation of precipitate (insoluble solid)
  5. Change in smell
  6. Change in state
  7. Sound or light produced

Oxidation vs Reduction

OxidationReduction
Gain of oxygenLoss of oxygen
Loss of hydrogenGain of hydrogen
Example: C + O2 → CO2 (C is oxidised)Example: CuO + H2 → Cu + H2O (CuO is reduced)

Memory aid: OIL RIG — Oxidation Is Loss (of hydrogen), Reduction Is Gain (of hydrogen)

Self-Check Questions

  1. Is dissolving salt in water a physical or chemical change? Why?
  2. Classify: Iron + Copper sulphate → Iron sulphate + Copper. What type of reaction is this?
  3. What is the difference between exothermic and endothermic reactions? Give one example of each.
  4. In the reaction CuO + H2 → Cu + H2O, which substance is oxidised and which is reduced?
  5. Write word equations for one example of each: combination, decomposition, displacement, double displacement.

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