Ya Hong Wu¹, Shan Ling Tong¹, Sheng Hu¹, Mao Ying Wu¹, Zhi Feng Hao¹, Yan Yan^1,

A typical kinetic experiment, the persulfate–iodide clock reaction, is selected as an example to illustrate applications of thermodynamic possibility and kinetic actuality in chemical reactions. In the experiment, the strongest reducer, sodium thiosulfate Na₂S₂O_3, cannot be directly oxidized by the strongest oxidizer ammonium persulfate (NH₄)₂S₂O₈, and this redox must be realized by an intermediate iodine I₂ [presenting in I₃^- anion, a weaker oxidizer than (NH₄)₂S₂O₈]. After I₂ molecules being reduced by Na₂S₂O₃ molecules to form I^- ions (a weaker reducer than S₂O₃^2-), the strongest oxidizer begins to oxidize the weaker reducer I^- ions to form I₂ molecules again, which is keeping on the redox circles until the stronger reducer Na₂S₂O₃ has been exhausted completely. Why the strongest reducer was not being oxidized by the strongest oxidizer? In this paper we attempt to explain this situation based on the chemical theories of thermodynamics and kinetics.

thermodynamics, kinetics, reaction rate, redox reactions