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March 29, 2017

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2ClO2 + 2OH- --> ClO2- + H2O

Experiment 1, M of [ClO2] = .060
M of [OH-] = .030
Rate of disappearance of ClO2 (M/s) = .0248


Experiment 2, M of [ClO2] = .020
M of [OH-] = .030
Rate of disappearance of ClO2 (M/s) = .00276


Experiment 3, M of [ClO2] = .020
M of [OH-] = .090
Rate of disappearance of ClO2 (M/s) = .00828

What is the reaction order of [ClO2]? Expain.

I have a bunch of these questions so if someone could walk me through this one I would appreciate it. Thanks.

  • Chem - ,

    I don't have time to go through the whole thing; however, here is how you do part of it. I think that will get it for you.
    First, look for two experiments in which there is the same concentration of ONE of the reactants. You see #1 has 0.03 for OH and #3 has 0.03 for OH. So let's pick those two to start.
    The reaction has this form for the rate.
    rate = k(ClO2)^x((OH^-)^y.
    We want to determine x and y, the exponents.
    rate 1 = 0.0248 = k(0.06)^x(0.03)^y
    rate 2 = 0.00276 = k(0.02)^x(0.03)^y
    Divide rate 1 by rate 2.
    You can do it on paper and follow through to keep me from typing a bunch of stuff.
    You see the 0.03^y term top and bottom cancel (that's why we chose one that had the same concentration for one of the reactants---they will cancel).You also see that k cancels (that's the rate constant). And 0.0248/0.00276 = 8.985 so now we have
    8.985 = (0.06)^x/(0.02)^x
    That is 8.985 = (0.06/0.02)^x
    That is 8.985 = (3)^x
    Now we take the log of both sides.
    log 8.985 = 0.9535
    log (3)^x = x*log 3 = x*0.477
    So now we have
    x*0.477 = 0.9535
    Then x = 0.9535/0.477 =1.9989 which rounds to 2. So the exponenet x = 2.
    Next you do the same thing but choose experiment 2 and 3 (because in those two reactions, (ClO2) are the same. Go through exactly the same procedure to determine y, the exponent for OH. The k cancels (top and bottom), the ClO2 cancels (top and bottom) leaving just the OH^y part. I determined y to be 1.0 so you will know if you did that part right if you find 1.0.
    When you know x and y, then choose ANY experiment you wish, plug in the value from the table of (ClO2) and (OH), plug in your values for x and y, and determine k. Then you will have determined x,y, and k, and those are the only unknowns in the experiment. I hope this helps.

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