Which rate law should I use to find the rate constant (K)?

Question

Which rate law should I use to calculate the rate constant (K)??

the reaction is a first order reaction, should I use:

Ln(A)= -kt + Ln [A]o

Or:

Rate = k [S2O8-][I-] where [S2O82-] and [I-] are the initial reactant concentrations.

Answer 1

Either one will work. Make sure it is a first order reaction though, otherwise ln(A) would be incorrect in the first equation.

What equation you use should depend on what information is given to you.