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Homework Help: Simple Ideal Gas problem

  1. Apr 27, 2009 #1
    1. The problem statement, all variables and given/known data

    Determine the number density of particles in a gas at STP (T=273, p=1atm)

    2. Relevant equations

    Answer is 2.68x1025

    3. The attempt at a solution


    I don't really understand what the "number density of particles" means please help!
  2. jcsd
  3. Apr 27, 2009 #2

    Andrew Mason

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    Science Advisor
    Homework Helper

    It means the number of gas molecules per unit volume. Mass density is mass per unit volume. For a gas, the pressure and volume depends on the number of molecules, not their mass.

    How many molecules of gas are then in a mole of the gas? How much volume does a mole of gas occupy at STP?

  4. Apr 27, 2009 #3
    hmm I can't quite get the right answer. V=22.4L and avagadros # is the molecules in one mole. How do I piece this together?
  5. Apr 27, 2009 #4
    Be careful of units here... when using PV=nRT what is the units of volume?

    So you know Avogadro's # is the number of molecules in one mole... so put the pieces together. As Andrew said, the number density the number of gas molecules per unit volume
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