Diffusion of gases


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Diffusion of gases

  1. 1. DIFFUSION OF GASES BY:rahul jain CLASS:12
  2. 2. What is diffusion? <ul><li>Diffusion occurs in liquids and gases but hardly at all in solids. </li></ul>Diffusion is the movement of particles that allows them to spread out and mix with other particles. For example, the smell of aftershave or perfume diffuses and is detected by people on the other side of the room. Use the particle model to explain these facts about diffusion: <ul><li>Diffusion happens more quickly for gases than for liquids. </li></ul><ul><li>Diffusion happens more quickly at warm temperatures than at cooler temperatures. </li></ul>
  3. 3. How do smells spread out? Where is the smell coming from and how does it spread out?
  4. 4. Diffusion animation 1
  5. 5. Diffusion animation 2
  6. 6. <ul><li>When the gases meet, they react to form a ring of ammonium chloride which is closer to one end of the tube than the other. </li></ul>Diffusion experiment cotton wool soaked in ammonia solution cotton wool soaked in concentrated hydrochloric acid Which gas particles diffuse faster, ammonia or acid, and why? By the time the gases meet, the ammonia particles have travelled further down the tube so they must have diffused at a faster speed. In this experiment, two gases diffuse towards each other in a sealed glass tube. gases meet here
  7. 7. The distribution of speeds for nitrogen gas molecules at three different temperatures 5.7 Velocity of a Gas The distribution of speeds of three different gases at the same temperature u rms = 3 RT M 
  8. 8. Gas diffusion is the gradual mixing of molecules of one gas with molecules of another by virtue of their kinetic properties. 5.7 NH 3 17 g/mol HCl 36 g/mol NH 4 Cl
  9. 9. Gas Diffusion relation of mass to rate of diffusion <ul><li>HCl and NH 3 diffuse from opposite ends of tube. </li></ul><ul><li>Gases meet to form NH 4 Cl </li></ul><ul><li>HCl heavier than NH 3 </li></ul><ul><li>Therefore, NH 4 Cl forms closer to HCl end of tube. </li></ul>
  10. 10. GAS DIFFUSION AND EFFUSION <ul><li>diffusion is the gradual mixing of molecules of different gases. </li></ul><ul><li>effusion is the movement of molecules through a small hole into an empty container. </li></ul>
  11. 11. Graham’s Law: Diffusion and Effusion of Gases <ul><li>Diffusion the process whereby a gas spreads out through another gas to occupy the space with uniform partial pressure. </li></ul><ul><li>Effusion the process in which a gas flows through a small hole in a container. </li></ul><ul><li>Graham’s law of Effusion the rate of effusion of gas molecules through a hole is inversely proportional to the square root of the molecular mass of the gas at constant temperature and pressure. </li></ul><ul><li>E.g. determine the molecular mass of an unknown compound if it effused through a small orifice if it effused 3.55 times slower than CH 4 . </li></ul><ul><li>E.g. A compound with a molecular mass of 32.0 g/mol effused through a small opening in 35 s; determine the effusion time for the same amount of a compound with a molecular mass of 16.0. </li></ul>
  12. 12. GAS DIFFUSION AND EFFUSION <ul><li>Graham’s law governs effusion and diffusion of gas molecules. KE=1/2 mv 2 </li></ul>Thomas Graham, 1805-1869. Professor in Glasgow and London. Rate of effusion is inversely proportional to its molar mass.
  13. 13. GAS DIFFUSION AND EFFUSION <ul><li>Molecules effuse thru holes in a rubber balloon, for example, at a rate (= moles/time) that is </li></ul><ul><li>proportional to T </li></ul><ul><li>inversely proportional to M. </li></ul><ul><li>Therefore, He effuses more rapidly than O 2 at same T. </li></ul>He
  14. 14. THE END