posted by Kimberky .
"What effect does doubling (S2O8)^2- have on the rate?" I don't understand that question. Could you please explain it?
You must be talking about kinetics. If the rate is r = k(S2O8-2) and it is a first order equation, then doubling the concn will double the rate.
If it is a second order equation, for example,
r = k(S2O8-2)2, then doubling concn will quadruple the rate. etc.