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Homework Help: Questions about kinetic theory

  1. Aug 30, 2007 #1
    May you professors please check part b of my work because my answer does not match the answer in the back of the book. Thank you.

    (a) What is the total random kinetic energy of all the molecules
    in 1 mol of hydrogen at a temperature of 300 K? (b) With what
    speed would a mole of hydrogen have to move so that the kinetic
    energy of the mass as a whole would be equal to the total random
    kinetic energy of its molecules?

    Answer to part (a):
    Since KE (total) = 1.5nRT, the total random kinetic energy is (1.5)(1)(8.314)(300) =
    3738.42 J/mol

    Answer to part (b):
    The atomic weight of hydrogen is 1.01 grams per mole
    So, the mass of one mole is 0.001 kg.

    We have to find the velocity
    By the kinetic energy formula,
    KE = (.5)(m)(v)^2
    (.5)(m)(v)^2 = 3738.42 J/mol
    So, v = 2734.3811 m/s

    However, the answer page in my booklet tells me that the correct answer for part b is 1.93 km/s. Please advise me and tell me what I did wrong. Thanks again.

  2. jcsd
  3. Sep 1, 2007 #2


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    Homework Helper

    The mass of one mole will be 2.02 g, since there are two hydrogen atoms in one hydrogen gas molecule.
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