Experimental Determination of us

The affinity —AG of the reaction N2 + 3H2 = 2NHj is expressed by definition in terms of ehemical potentials etc., as 

The left-hand side vanishes in equilibrium of the reaction, while the first term on the right-hand side is —kT In K, where K = 

Unidirectional rate of the reaction is determined by means of isotopic tracer as follows. Let x or be the atomic fraction of in nitrogen molecules or in ammonia molecules, respectively, in gas and the number of nitrogen molecules present in a closed vessel at time t. The rate of transfer of from nitrogen into ammonia is expressed as —2d n x )ldt or, alternatively, as 2a F+ — 2x V, hence 

The validity of the above method of F determination rests upon the assumption that the transfer of N proceeds solely through the rate-determining step. 

We have in general different isotopic tracers available for the determination of unidirectional rate, hence of Vg (31,32). In the case of water gas shift reaction dealt with in II,D,2, for instance, the unidirectional 

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