Apparent Activation Energy of a Stepwise Process

The thermodynamic form of kinetic equations aUows us to easily find the apparent activation energy, EaS, for the stationary occurrence of stepwise processes, especiaUy in the case of their kinetic irreversibility. For instance, if stepwise process (1.54) goes from left to right and is kineticaUy irrevers ible in whole—that is, R P—and if Sum is the smaUest quantity of aU 8 in the transformation chain, then 

By definition, the apparent activation energy of a process is determined by the equation 

Y(R Y P) in the case of a left-to-right process with the elementary reaction Y P as the rate-limiting stage. Cases a and b relate to different enthalpies of the transition state formation. 

Notice that equation (1.59) meets the commonly known rule that the apparent activation energy of a consecutive process equals the activation energy of the rate Hmiting step minus the sum of the heats (or plus sum of standard enthalpies, 2 AfH°) of the preceding stages, which are treated as being in equilibrium. 

In fact, activation energy of a kineticaUy irreversible reaction i equals E, = AfHf - AfH° + RT, 

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