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Homework Help: Gases and Average Speed

  1. Apr 27, 2012 #1
    1. The problem statement, all variables and given/known data

    The gases in this room include oxygen (molar
    mass 32 g), nitrogen (28 g), water (18 g), and
    carbon dioxide (44 g). Which type of molecule has
    the highest average speed?

    A) O2
    B) N2
    C) H2O
    D) CO2
    E) They have the same average speed.

    2. Relevant equations

    1/2 mv^2 = 3/2 kT

    3. The attempt at a solution

    Is the answer water because it's mass is the smallest?
  2. jcsd
  3. Apr 27, 2012 #2
    The molecular speed of gases at constant temperature varies inversely with the square root of the molecular mass. So the lightest molecule will go the fastest.
  4. Apr 27, 2012 #3
    Thanks for replying. Sorry if it seemed obvious - I'm doing review problems without looking at the answers.
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