Experiment 5.6 Marcus Theory Theoretical Calculation of the

EXPERIMENT 5.6 MARCUS THEORY THEORETICAL CALCULATION OF THE OUTER-SPHERE RATE CONSTANT, kos, FOR THE REACTION BETWEEN [Co(ox)2(EN)] AND [Co(en)3]2+11 

In this experiment, the outer-sphere electron transfer rate constant for the reaction between [Co(en)3]2+ and [Co(ox)2(en)] will be calculated using Marcus theory. The calculated value will then be compared with the rate constant determined in Experiment 5.5. 

Because outer-sphere reactions are mechanistically simple (no bond making and breaking occurs), they are amenable to theoretical treatment. Marcus theory, which allows the prediction of outer-sphere electron transfer rates between two species, was developed in the 1960s by Rudolph Marcus, who won the Nobel prize for his work in 1992. His simple equation is given below  

KAB is the equilibrium constant for the overall reaction, and fAB = (log KAB)2/ 4 log(kAAkBB/Z2). Z2, a collision term, and for uncharged particles, is 1011 M-1 s 1. Modifications must be made for charged species. 

You will notice that the Marcus equation brings together kinetics and thermodynamics. For the system you will be studying, the reaction takes place in what is called the normal  

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