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Homework Help: Celsius to Kelvin conversion problem (Kinetic theory)

  1. Feb 19, 2016 #1
    1. The problem statement, all variables and given/known data
    Find the temperature T that allows the rms speed of a gas to be equal to another gas with T=47°C.
    The molecular mass of the first gas is 64, and the molecular mass of the second gas is 32.

    2. Relevant equations
    [tex]v_{rms}= \sqrt{\frac{3RT}{M}}[/tex]

    3. The attempt at a solution
    The problem is actually very easy. It's actually really simple to conclude that
    [tex]T_1=2T_2[/tex]. However, my problem arises when actually replacing the given temperature.
    If I take the second temperature to equal 47°C, then the first temperature is equal to 94°C. And converting that to kelvin gives 367.15 K.
    However, if instead I use directly the temperature in K (47+273.15), then my answer becomes 640.3 K.
    Which one is right? I assume the second one because in order for the equation to make sense, T needs to be expressed in K. I'd like to be sure, however.
  2. jcsd
  3. Feb 19, 2016 #2


    User Avatar

    Staff: Mentor

    Well, that depends which gas you label 1, and which you label 2.

    Think about this: what if the temperature was 0 °C instead of 47 °C.
  4. Feb 19, 2016 #3
    That would make the other temperature zero. Understood! Thank you very much.
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