Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Kinetic theory: gas/pressure

  1. Jun 20, 2011 #1
    1. The problem statement, all variables and given/known data

    An ideal gas is kept in a container of constant volume. The pressure of the gas is also kept constant
    (a) If the number of molecules in the gas is doubled, does the rms speed increase, decrease, or stay the same?
    (b) If the initial rms speed is 1300 , what is the final rms speed?

    2. Relevant equations

    PV=nRT...I think

    3. The attempt at a solution
    For part I, I believe the rms speed decreases. So if the only thing changing is the number of molecules wouldn't doubling the molecules cause rms to decrease by half? I know the answer is no, because the computer said so, I'm just not sure why it's wrong. And how much does it decrease then?
  2. jcsd
  3. Jun 20, 2011 #2
    If the volume and the pressure must remain constant, the only way to get in more molecules is cooling the gas, and let in more gas to keep the pressure constant.

    If the original tempererature was T, what is the new temperature?

    After you've found it use

    [tex] v_{rms} = \sqrt { \frac {3 R T} {m} } [/tex]

    where m is the mass of one mole of the gas molecule
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook