Nature and State of the Reactant

Chemical identity changes the energy cost of reacting. Every reaction involves breaking some of the reactant's existing bonds and forming new ones in the product; the net energy this costs is fixed by the specific chemical NATURE of the reactant, so genuinely different reactants react at genuinely different speeds even under otherwise identical conditions. A direct comparison from volumetric analysis: oxidising ferrous ammonium sulphate (FAS, containing $Fe^{2+}$) with $KMnO_4$ proceeds readily at room temperature, while oxidising oxalate ion with the SAME $KMnO_4$ is noticeably slower -- slow enough that the oxalate-permanganate titration is conventionally run with external heating to around $60^\circ$C just to get a workable rate. …