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ICSE Class 7 Chemistry Question 8 of 11

Language of Chemistry — Question 8

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Question 8

Give examples of exothermic reactions i.e. heat evolved in each of the following:

(a) reaction between a solid and a liquid

(b) reaction between two gases

Give two examples of exothermic reactions seen in everyday life.

Answer

(a) CaO + H2O ⟶ Ca(OH)2 + Δ

(b) 2H2 + O2 ⟶ 2H2O + Δ

Two examples of exothermic reactions from everyday life are:

  1. Human Body — Many chemical reactions in our body are exothermic and provide energy to survive.
  2. Setting of Cement — Cement setting liberates heat hence concrete structures are set slowly.

ICSE Class VII Chemistry Chapter 4 12 Marks

Language of Chemistry — Quick Study Guide

Chemical symbols, formulae, and equations are the language chemists use to describe substances and reactions.

Key Concepts

  • Chemical symbol: Shorthand for an element (first letter capital, second lowercase)
  • Chemical formula: Shows types and numbers of atoms in a molecule
  • Cross-multiplication: Write symbols → valencies → cross → simplify
  • Balanced equation: Same number of each atom on both sides
  • Combination reaction: A + B → AB
  • Decomposition reaction: AB → A + B

Latin-Origin Symbols to Memorise

Na (Sodium), Fe (Iron), Au (Gold), Ag (Silver), K (Potassium), Cu (Copper), Hg (Mercury), Pb (Lead), Sn (Tin)

Exam Tips

  • Never change subscripts when balancing — only change coefficients
  • Use brackets for polyatomic ions when subscript > 1
  • Practice writing formulae using cross-multiplication daily
  • CO ≠ Co (carbon monoxide vs cobalt)

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