9.4 Effusion and Diffusion of Gases

9.4 Effusion and Diffusion of Gases

  • Susan Solomon's research has helped determine the cause of the ozone hole.
  • If you've ever been in a room where a piping hot pizza was delivered, you've been made aware of the fact that it can quickly spread throughout a room, as evidenced by the pleasant smell that soon reaches your nose.
    • The gasses travel at great speeds, but they collide with each other and travel in many different directions before reaching their destination.
    • Billions of particles will be created per second at room temperature.
  • A net movement of species from high to low concentration areas takes place when the gaseous atoms or molecule move randomly.
  • After the stopcock is opened, more H2 molecule move to the O2 side than O2 molecule move to the H2 side.
  • The concentration gradient, the amount of surface area available for diffusion, and the distance the gas particles must travel are some of the factors that affect the rate.
    • The rate of diffusion equation shows that the time required for diffusion is proportional to the rate.
  • Gas molecule dispersal occurs in a container.
    • When a gas passes through an opening that is smaller than the mean free path of the particles, it causes efffusion.
    • Only one particle can pass through at a time.
  • If a mixture of gases is placed in a container with porous walls, the gases effuse through the small openings in the walls.
    • The lighter gases pass through the small openings at a higher rate than the heavier ones.
  • A balloon filled with air is full.
    • A balloon filled with helium is partially deflated because the smaller, light helium atoms are easier to see in the rubber than in the air.
  • Hydrogen effuses four times faster than oxygen.
  • Nitrogen gas effuses at a rate of 79 mL/s at certain pressures and temperatures.
  • This is an example of how determining times and rates differ.
  • It takes 243 s to get through a tiny hole.
  • To remember how rate relates to time as well as how it relates to mass is important to resist the temptation to use the times directly.
  • Since Ne is lighter than Xe, the time of effusion for Ne will be smaller than for Xe.
  • A party balloon is inflated to 23 of its original volume in eight hours.
  • This is the final example showing how to calculate the mass from the data.
  • An unknown gas effuses 1.66 times faster than CO2.
  • The only gas with this mass is CH4.
  • Hydrogen gas effuses through a porous container at a faster rate than an unknown gas.
    • Estimate the mass of the gas.
  • Nuclear power plants and weapons can be enriched with gaseous diffusion.
  • The kind of uranium that is "fissile" is 0.72% of 235U.
    • Nuclear bombs need even higher concentrations of fuel.
    • Graham's law can be used to enrich uranium to desired levels.
    • In a gaseous enrichment plant, the only compound that is volatile enough to work is slowly pumped through large cylindrical vessels.
    • The other side of the barrier is not being evacuated.
    • The heavier 238UF6 molecule diffuses through the barrier a little faster than the lighter 235UF6 molecule.
    • The residual gas is slightly deplete and the gas that has passed through the barrier is slightly enriched.
    • There is a small difference between the weights of 235UF6 and 238UF6 in one diffuser.
    • The desired level of enrichment can be achieved by connecting many diffusers in a sequence of stages.