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Homework Help: Chemical Reaction Engineering homework

  1. Apr 29, 2017 #1
    1. The problem statement, all variables and given/known data
    The decomposition of phosphine 4PH3(g) + P4(g) + 6H2(g) is first-order with respect to phosphine with a rate constant k = 0.0155 s-l at 953 K. If the decomposition occurs in a constant-volume batch reactor at 953 K, calculate, for 40% conversion of PH3,

    (a) the time required, s;
    (b) the mole fraction of H2 in the reaction mixture.

    2. Relevant equations
    Ca= Ca0 (1-Xa)
    3. The attempt at a solution

    a) i attempet do apply the equation for spacial time im batch reactors:
    -dCa/dT = kCa
    ∫-dCa/Ca =∫kdT
    -ln(Ca/Ca0) = kT
    -ln (Ca0(1-Xa)/Ca0) = kT
    -ln (1-Xa) = kT --> -ln (1-0,4) = 0,0155 * T --> -ln(0,6)/0,0155 =T
    T = 32,96 s
    b) i have no idea
    Last edited: Apr 29, 2017
  2. jcsd
  3. Apr 30, 2017 #2


    User Avatar
    Homework Helper
    Gold Member

    So of the total original molecules of PH3 0.6 of them are still PH3, and of the 0.4 that have reacted each one has become 1.5 molecules of H2 and ¼ of P4 according to your formula (which should have a → instead of a + ) and you have any difficulty in finding what fraction H2 molecules are of the total? :))
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