Diffusion

• Diffusion


  The process by which different gases or different liquids mix and is due to the random motion of their particles
• Diffusing particles move


  From an area of high concentration to an area of low concentration
• Eventually the concentration of particles is even as they spread out to occupy all of the available space
• Diffusion happens on its own and no energy input is required although it occurs faster at higher temperatures
• Diffusion of potassium manganate(VII), KMnO4, in water


  • After a few hours the concentration of KMnO4 is the same throughout the solution
• Diffusion


  • Occurs much faster in gases than in liquids as gaseous particles move much quicker than liquid particles
• At the same temperature, different gases do not diffuse at the same rate


  This is due to the difference in their relative molecular masses
• Lighter gas particles can travel faster and hence further, therefore the lower its relative mass the faster a gas will diffuse
• Reaction between ammonia, NH3, and hydrogen chloride gas, HCl, inside a long glass tube


  • Where the two gases meet a white smoke of ammonium chloride, NH4Cl, is formed
  • This does not occur in the middle of the tube as you might expect, but much closer to the end with the hydrogen chloride (Mr = 36.5) and the ammonia (Mr = 17) molecules are smaller and lighter
  • NH3 molecules have less mass than the HCl molecule, so diffuse faster, hence the product (a white smoke of NH4Cl) forms closer to the end where the HCl is