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Homework Help: Some basic homework help

  1. Feb 13, 2004 #1
    Can anyone help me solve these two problems?
    1. A tank of compressed air of volume 1.0 m^3 is pressurized to 40 atm at T= 273. A valve is opened and air is released until the pressure in the tank is 23.0 atm. How many air molecules were released?

    2. About how long will it take a perfume molecule to diffuse a distance of 7.00 m in one direction in a room if the diffusion constant is 1.00 x 10^-5 m^2/s? Assume that the air is perfectly still- there are no air currents.
     
  2. jcsd
  3. Feb 13, 2004 #2

    ShawnD

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    Use the formula
    PV = nRT

    P is pressure (pascals or kilopascals, I can't remember), V is volume in litres, n is the number of moles, R is the gas constant, T is temperature in kelvin
    Figure out how many moles of air molecules were there at start then how much after. Just subtract the two.
     
  4. Feb 13, 2004 #3
    P should be in atmospheres.
     
  5. Feb 13, 2004 #4

    ShawnD

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    Depends which R you use.
     
  6. Feb 14, 2004 #5
    Use Pascals and 8.31 for R
     
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