# Half Life for a second order reaction

1. Dec 9, 2006

### preet

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.

Thanks
Preet

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2. Dec 9, 2006

### GCT

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.