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Homework Help: Kinetics question (Chemical engineering)

  1. May 31, 2017 #1
    • Thread moved from the technical forums, so no Homework Template is shown

    I have a question regarding this question that I have to answer. It is about the kinetics of a substance X whose product is 2Y. It is in Swedish and here is the translation:

    The absorbance of a 0,030M-solution of X was calculated with the help of a Spectrometer. The Spectrometer was calibrated to measure the absorbance of the product Y in the following reaction: X(g)-->2Y(g). The koncentration of Y was measured after a minute and every minute consequentially in 23 minutes. The graph shows these concentrations:

    The question is, calculate the reaction rate constant.

    Now to do this, in my opinion and hunch, is we have to know the reaction order and to find it out I usually use a calculator to make a graph of the concentration vs. time, ln(concentration) vs. time and 1/(concentration) vs. time to see whether we deal with a 0, 1 or 2nd order reaction. But I can't seem to get equal amounts of points to make a graph, hence I am stuck :/.
    Would anyone please kindly help me with this question?
  2. jcsd
  3. May 31, 2017 #2

    jim mcnamara

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    Staff: Mentor

    @Beyar I do not think this is homework. Is that correct?
  4. May 31, 2017 #3
    This is homework, indeed. I've been having issues with it for a while now and made several calculations and still get the wrong answer.
  5. May 31, 2017 #4


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    Science Advisor

    What do you mean by "can't get equal amount of points to make a graph"?

    For what data are those relationships valid? Can you use them with your given [Y]-t data?
  6. Jun 1, 2017 #5


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    These functions of concentration of what against time? X or Y? For your points after about 10 minutes you are so close to equilibrium or to zero [X] , i.e. essentially no reaction happening, that you cannot use them in your kinetics graphs - you cannot do kinetics where nothing is changing!
    Last edited: Jun 1, 2017
  7. Jun 1, 2017 #6
    Against the concentration of Y.
  8. Jun 1, 2017 #7


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    It makes more sense to use [X] though only for values that are significantly different from zero.
    Last edited: Jun 1, 2017
  9. Jun 1, 2017 #8
    Assume that the reaction is 1st order, and that the original concentration of Y is zero. What are the concentrations of X at the various times?
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