Bright Tutorials Bright Tutorials
ICSE Class 8 Chemistry Question 12 of 15

Chemical Reactions — Question 1

Back to all questions
1
Question

Question 5

Give balanced equations for -

(i) A direct combination reaction involving two elements, one of which is a non-metal.

(ii) A thermal decomposition reaction involving heat on limestone [calcium carbonate].

(iii) An electrolytic decomposition reaction involving a neutral liquid.

(iv) A displacement reaction involving a metal above hydrogen in the activity series with copper [II] sulphate solution.

(v) A double decomposition neutralization reaction involving an acid & a base.

(vi) A white precipitate obtained during a double decomposition reaction involving a silver salt with a sodium salt.

Answer

(i) C + O2 ⟶ CO2

(ii) CaCO3 →Δ\xrightarrow{\Delta} CaO + CO2

(iii) 2H2O →currentelectric\xrightarrow[\text{current}]{\text{electric}} 2H2 + O2

(iv) Zn + CuSO4 ⟶ ZnSO4 + Cu

(v) HCl + NaOH ⟶ NaCl + H2O

(vi) AgNO3 + NaCl ⟶ AgCl ↓ + NaNO3

Chemical Reactions - Study Guide | Bright Tutorials
BRIGHT TUTORIALS
Bright Tutorials Logo
BRIGHT TUTORIALS
ICSE Class VIII | Academic Year 2026-2027
9403781999
Excellence in Education
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.

Bright Tutorials | Hariom Nagar, Nashik Road | 9403781999 | brighttutorials.in