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3 Questions regarding reaction kinetics- please help me out.

  1. Jul 10, 2014 #1
    Hi I need some help understanding reaction kinetics, and I’m trying to get an overview, so I’d really appreciate some help. I have 3 individual/quite unrelated questions, if you have time to answer one that would be very much appreciated.

    1. In what situations dos the Definition of the reaction rate for a general reaction Hold true?

    aA + Bb --> pP+qQ

    -(1/a)*(d[A]/dt)= -(1/b)*(d/dt) = -(1/p)*(d[P]/dt) = -(1/q)*(d[Q]/dt)

    I would assume this definition only holds true when all the rates are equal, so this does not apply for reactions where the rate of A is different from the rate of B (if this is possible)

    2. If the rate of A is slower than the Rate of B, would they then not be comsumed at the same RATE because A would be the limiting factor, the equation -(1/a)*(d[A]/dt)= -(1/b)*(d/dt) holds true for all reactions?

    3. Is it true that if the rate law for A + B --> C +D is givn by -d[A]/dt = k[A]^n^m with respect to A, then it might be different with repsect to B? So -d/dt might be different (slower or faster) than -d[A]/dt, so the -d[A]/dt=-d/dt = k[A]^n*^m only holds true for elementary reactions, while for complex reactions the rate law for -d[A]/dt could be equal to k[A] raised to a first order while -d/dt could be equalt to k[A]^2^1 (something different?)
  2. jcsd
  3. Jul 10, 2014 #2


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    Staff: Mentor

    It is not possible. I already told you somewhere else that we use stoichiometric coefficients to make sure rates of the reaction for all substances involved are identical.
  4. Jul 10, 2014 #3
    Hi borek, yes i was a bit confused on what question you were answering but now it seems more clear to me: What you are saying is that No matte what reaction we have (Zero order, first order, second order, complex) the equation -(1/a)*(d[A]/dt)= -(1/b)*(d/dt) = -(1/p)*(d[P]/dt) = -(1/q)*(d[Q]/dt) is true? and in some cases the rate of any of the reactants might display the following relationship = k[A]^m^n (for complex reactions) and in elementary reactions the orders of the reaction equals the koefficients of the reactants?

    If this is a correct understanding, I'm really happy :)
  5. Jul 10, 2014 #4
    Ohh yes an just to make sure it's 100% clear for me:

    If -(1/a)*d[A]/dt)=k[A]^m^n

    Then This must also be true


  6. Jul 10, 2014 #5


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    Staff: Mentor

    Yes, yes, yes & yes.
  7. Jul 10, 2014 #6
    Thank you very much Borek - Now I'm really happy :D
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