[greentea11]

Question attached

so for the first bit i've plotted ln
 vs time to get a linear slope, hence it is first order

then for the second bit,
this means rate = k
[F]

and ln
[F°]/[F][Br°] = k([Br°] - [F°])t

so If I could plot this graph, the slope would be = k([Br°] - [F°])
and thus I could find k

However, this method is flawed for this question, as I only have the initial concentration of F, [F°] = 4 x10^-9, and no more values of [F]

Any hints how I can find k for this second order reaction, from the information given? Ideas appreciated

[mjc123]

I don't know where you get k([Br°]-[F°]) from. [Br°] is presumably zero, so this is meaningless.
You do know the values of [F] versus time, as you know the stoichiometry of the reaction, so [F]₀ - [F]_t = [Br₂]₀ - [Br₂]_t
But since [F]₀ >> [Br₂]₀, the concentration of F remains approximately constant at [F]₀. This is the basis of the first part of the question - the reaction is pseudo-first-order, as the concentration of F effectively doesn't change.
Can you obtain an apparent first-order rate constant for the disappearance of Br₂, and relate this to [F]₀ and the true second-order rate constant?