CIE IGCSE Physics

Revision Notes

2.1.4 Evaporation

Cooling by Evaporation

  • Evaporation is a change in state of a liquid to a gas that can happen at any temperature from the surface of a liquid

Evaporation table, IGCSE & GCSE Physics revision notes 

  • The molecules in a liquid have a range of different energies:
    Some have lots of energy, others have very little
  • Evaporation occurs when more energetic molecules near the surface of the liquid have enough energy to escape

 

Evaporation, IGCSE & GCSE Physics revision notesEvaporation occurs when more energetic molecules near the surface of a liquid escape

 

  • When this happens energy is lost from the liquid:
    • The average energy of the remaining molecules decreases
    • This means that the temperature of the remaining liquid will also decrease

 

 

Exam Question: Cooling by Evaporation

Extended Only

Factors Affecting Evaporation

  • A number of factors affect the rate of evaporation:
    • The temperature of the liquid – At higher temperatures, more molecules have enough energy to escape
    • The surface area of the liquid – If the liquid has a greater surface area there will be more area from which the molecules can escape
    • The movement of air across the surface of the liquid – The presence of a draft can help to remove less energetic molecules (which might not have quite enough energy to escape) from the liquid
  • The process of evaporation can be used to cool things down:
    • If an object is in contact with an evaporating liquid, as the liquid cools the solid will cool as well
    • This process is used in refrigerators and air conditioning units

 

 

Exam Question: Factors Affecting Evaporation

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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