[Radu]

        http://icho2014.hus.edu.vn/document/01-24-2014%20IChO46-Preparatory.pdf

       My question is about 12.2
                    2N₂O₅ 4NO₂ + O₂

      I am given a table of concentrations of N₂O₅ at different times from the beginning of the reaction.
     I am supposed to plot ln([N₂O_5(t)/[N₂O₅⁰) versus time or {[N₂O_5(t)/[N₂O₅⁰ - 1} versus time. I don't know what {a/b - 1} means. Thanks! :d

[Big-Daddy]

Think about how this works. I cannot generally integrate d[A]/dt = -k[A]ⁿ, because n=1 necessitates a different method of integration from n≠1. By plotting the first graph, you prepare yourself for a straight line if the reaction order is 1; by plotting the second graph, you prepare yourself for a straight line if the reaction order is 2. Go from the 0th, 1st, 2nd order integrated laws:

n=0  [A]=[A]₀-kt
n=1  [A]=[A]₀*e^-kt
n=2  [A]=[A]₀/(1+[A]₀kt)

By the way these are the 0 to 2nd order laws for reactants with stoichiometric coefficient 1. For IChO you will probably have to be aware of how to reach analogous formulae for products, and with any stoichiometric coefficient.

[Radu]

 Yes, I have already done that, I assumed this was what they want from us. I just read through the problem again and I found they mistyped when they said [N₂O₅]_(t)/[N₂O₅]₀ - 1 , it was actually [N₂O₅]₀/[N₂O₅]_(t) - 1 to work, and the latter was mentioned later in the problem.
      Thanks for the tips!

[Benzene]

how are the constants "K" derived?