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Homework Help: Half Life for a second order reaction

  1. Dec 9, 2006 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations

    HalfLife = 1 / k*[A]i

    where k is the rate constant and [A]i is the initial concentration of a reactant A.

    3. The attempt at a solution

    I don't have enough information to attempt this problem. I don't know what to do with the partial pressure of O2 (is it part of the reactants?) If it is, then does the reaction become third-order?

    I also don't see the point of having HClO4 in this problem... does it change anything?

    By using the given values of k and [Fe] and plugging into the equation, you get 2702.7 atm hours... I think this is wrong because I didnt use the partial pressure of O2 at all...

    One final thing, the units by just using the half life equation give atm*hours... and if you divide by the pressure you get the correct unit, just hours. Is this the correct thing to do (the result is 13 513 hours)...

    I just want to know whether I'm in the right direction.


    Attached Files:

    • FE.jpg
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  2. jcsd
  3. Dec 9, 2006 #2


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    Science Advisor
    Homework Helper

    Fe2+ does react with HClO4, assuming you can ignore the formation
    of Fe(OH)2, you need to incorporate the rate dyanmics of this reaction and that of the Fe2+ reacting with oxygen gas. You need to put everything in terms of how the Fe2+ is depleted.
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