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ICSE Class 7 Chemistry Question 2 of 11

Language of Chemistry — Question 2

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Question 2

State four conditions necessary for chemical reactions to take place.

Answer

The four conditions necessary for chemical reactions to take place are:

  1. Close contact: For a chemical reaction to take place the reactants must come into close contact i.e. they should be mixed.
  2. Solution form: Some substances react with each other only when they are mixed in solution form.
  3. Heat: Some reactants need to be heated to undergo a chemical change.
  4. Light: Some reactions take place in the presence of light.

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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