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chemistry igcse acapprinted 5 · PDF 5
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5
Melting Point
Boiling Point
Pure Water
0
100
Impure Water
-2
102
Diffusion and Evaporation
• Diffusion is when liquids or gasses mix due to their random movement.
• In diffusion, particles of the liquid/gas move from an area of higher concentration to an area of
lower concentration.
• There are two factors that affect the rate of diffusion
1. Temperature: The higher the temperature, the faster particles will diffuse and vice versa.
2. Mass of particles: The larger a particle’s Relative Atomic/Molecular mass is, the slower it will
diffuse and vice versa.
For example, ammonia (NH3) will diffuse faster than hydrogen chloride (HCl) as the Relative
Molecular Mass (Mr) of is 17 and the Mr of HCl 36.5
• Evaporation is when a liquid changes its state from a gas, but at any given temperature. Unlike
boiling, evaporation does not require a fixed temperature to take place.
• Evaporation only occurs at the surface of the liquid while boiling occurs throughout the liquid.