[ALMOS7]

So I did a lab and I am supposed to calculate the initial rate of reaction. I only have the time, the molarity, and the balanced equation.

2I + S₂O₈^-2 -> I₂ + 2SO₄²
 
               [I^-]        [S₂0₈]
Trial 1    .03846      .03846        Time: 95.5 s
Trial 2    .03846      .01923        Time: 224 s
Trial 3    .01923      .03846        Time: 201.1 s

I calculated the concentrations by using M1V1=M2V2. We were only given the volume of our solution and it's concentration, so i figured after mixing it would be diluted, and using this equation is appropriate. (am I right?)

Now I'm not sure how to calculate the initial rate and the rate constant, k. Do i just use that equation rate = (-1/α)(ΔA/Δt) where α is the coefficient on either KI or S208, A is one of the reactants, and t is time ?

 the thing is there is I and S208 on the reactant side side....do i use the rate of the slower reaction as my initial rate?

[ALMOS7]

woops forgot to include that the I and the S208 were mixed together, and those are the concentrations of each after they were mixed, and the time is for the time it took for the solutions to react with eachother.