Apparent activation energies and kinetic isotope effects using the reaction order approach

4 Apparent activation energies and kinetic isotope effects using the reaction order approach 

In eqn. (54),feapp was considered to be a constant. In the determination of apparent activation energies and kinetic isotope effects, it is the variations in feapp as reflected in variations in vc with temperature or isotopic substitution while the concentrations are held constant that must be determined. The appropriate relationship becomes 

The important feature of this equation is that any changes in feapp brought about by changes in temperature or isotopic content of the reagents must be exactly balanced by the same degree of change in the normalized sweep rate (a) in order for (or f [) to remain constant. 

Kinetic isotope effects can also be evaluated using eqn. (67). Most often, it is deuterium kinetic isotope effects, (fcappW appta and the appropriate relationship is 

The isotopic label may be either in the substrate A or in additional reactant X. 

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