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ICSE Class 8 Chemistry Question 13 of 15

Chemical Reactions — Question 2

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Question

Question 6

State what is meant by 'reactivity series of metals'. With reference to -

(a) Water

(b) Acids

explain with suitable examples how the reactivity of the metals could be differentiated.

Answer

Reactivity series of metals is a series of arrangement of metals in decreasing order of their chemical reactivity. Metal reactivity series is listed below:

Activity
Series
K
Na
Ca
Mg
Al
Zn
Fe
Pb
*[H]
Cu
Hg
Ag
Pt
Au

Differentiating reactivity of the metals with reference to Water & Acids:

Reaction
with		MetalsObservationEquation
WaterK & NaReact violently with cold water2K + 2H2O ⟶ 2KOH + H2
CaReacts less vigorously with cold waterCa + 2H2O ⟶ Ca(OH)2 + H2
Mg to FeReact smoothly with water [steam]3Fe + 4H2O ⇌ Fe3O4 + 4H2
Below [H]Do not react with water or steam displacing hydrogen from it. 
AcidsK & NaReact explosively with HCl or dil. H2SO42K + 2HCl ⟶ 2KCl + H2
Ca to FeReact less vigorously with decreasing vigour with dil. HCl or dil. H2SO4Ca + 2HCl ⟶ CaCl2 + H2
Below [H]Do not react with dil. acids, displacing hydrogen from it. 
Chemical Reactions - Study Guide | Bright Tutorials
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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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