Melting ice. Image credit flemox.com

Melting ice. Image credit flemox.com

ZIMSEC O Level Combined Science Notes: Changes in state

When a solid item is heated the forces of attraction between the particles become weaker

as a result the particles move more quickly

  • The particles gain more kinetic energy
  • the solid item melts
  • the particles move from their fixed positions
  • as a result the solid changes into a liquid
  • this process is known as melting
  • if the liquid is heated further the particles move faster and apart from each other
  • the liquid turns into a gas
  • That is the liquid vapourises
  • if heat is removed and the gas is allowed to cool it condenses
  • the particles move closer together and move more slowly and thus the gas turns into a liquid
  • if the liquid is cooled further it solidifies
  • that is it turns into a solid
  • the particles in a solid have less kinetic energy
  • they thus move less because the forces of attraction between them is stronger
  • solidifaction-is when a liquid turns into a solid
  • vapourisation-when a liquid turns into a gas
  • condensation-is when a gas turns into a liquid
  • melting-is when a solid turns into a liquid

sublimation

Dry ice subliming. Image credit MediaWiki

Dry ice subliming. Image credit MediaWiki

  • when some solids are heated they do not melt
  • instead they turn into a vapour immediately without turning into liquid first
  • for example when gray iodine crystals are heated they turn into a purple vapour
  • this is known as sublimation
  • sublimation-is when a solid turns directly into a vapour

To access more topics go to the Combined Science Notes page.


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