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ICSE Class 7 Chemistry Question 12 of 13

Physical and Chemical Changes — Question 4

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Question 4

Fill in the blanks with the correct words for each of the statements given below:

  1. Sublimation is ............... [considered/not considered] a change of state of matter.

  2. Sublimation involves a ............... [chemical/physical] change.

  3. During sublimation a solid on heating turns directly into ............... [liquid/vapour] & on cooling back to ............... [solid/liquid].

  4. Ammonium chloride, a sublimable solid undergoes ............... [synthesis/dissociation] on heating.

  5. Sublimation of iodine is an example of ............... [physical/chemical] change.

Answer

  1. Sublimation is considered a change of state of matter.

  2. Sublimation involves a physical change.

  3. During sublimation a solid on heating turns directly into vapour & on cooling back to solid.

  4. Ammonium chloride, a sublimable solid undergoes dissociation on heating.

  5. Sublimation of iodine is an example of physical change.

ICSE Class VII Chemistry Chapter 2 12 Marks

Physical and Chemical Changes — Quick Study Guide

Changes around us are classified as physical (no new substance formed) or chemical (new substance formed). Understanding the difference is fundamental to chemistry.

Key Definitions

  • Physical change: No new substance formed, usually reversible (e.g., melting ice, dissolving sugar)
  • Chemical change: New substance formed, usually irreversible (e.g., burning, rusting, cooking)
  • Exothermic: Reaction that releases heat (e.g., burning fuel)
  • Endothermic: Reaction that absorbs heat (e.g., photosynthesis)

Six Signs of Chemical Change

Colour change, gas evolution, temperature change, precipitate formation, smell change, light/sound emission.

Exam Tips

  • Burning a candle = BOTH physical and chemical change
  • Dissolving salt/sugar in water = physical change (recoverable)
  • Not all physical changes are reversible (tearing paper)
  • Learn the comparison table (6 differences) thoroughly

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