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Homework Help: Reaction Mechanism Predictions

  1. Aug 27, 2011 #1
    A chemical Reaction A-->B is carried out in a closed vessel. The following data are taken for the concentration of A, Ca (g/L), as a function of time, t(min), from the start of the reaction. A proposed reaction mechanism predicts that Ca and t should be related by the expression

    ln (Ca-Cae)/(Ca0-Cae)=-kt

    where k is the reaction rate constant

    Do the data (see attached file) supports this prediction? If so, determine the value of k. (Use a semilog plot in your solution for this problem)

    Can someone explain to me what using a semilog plot means? And, maybe give me a hint on how to start this problem please.... Thank you!

    Attached Files:

  2. jcsd
  3. Aug 27, 2011 #2
    A [2-D] semilog plot has a logarithmic scale for only one axis.

    To start the problem, I would exponentiate to get rid of the logarithm. Re-arange to solve for CA, and determine if the function's initial value and the value it approaches agree with the plot.

    You should know what the plot of [itex]f(t) = Ce^{-kt} + D[/itex] would look like.

    Know that if k is positive, the term [itex] Ce^{-kt} [/itex] will approach zero as t becomes larger.

    You should be able to indentify (in terms of C and D):

    • the value of this function when t = 0
    • the value it approaches as t becomes larger
  4. Sep 4, 2011 #3
    Thank you so much for your help!!
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