Addition reactions, equilibria and alkyl radical heats of formation

5 Addition reactions, equilibria and alkyl radical heats of formation Rate coefficients for addition reactions such as 

Kinetic studies of the forward and reverse reactions (either under isolated conditions or during direct equilibration) can therefore be used to determine nd from this the heat of formation of the alkyl radical, 

Af// g(R)- Alkyl radical heats of formation are of considerable importance because they are linked to the C—H bond strength of the corresponding 

As the temperature of the system rises it is noted that the decays of the atomic species in the presence of excess alkene are no longer exponential, but show a biexponential decay. At high temperatures the rate of alkyl radical dissociation occurs on the same timescale as the addition reaction and equilibrium is established. The two portions of the biexponential decay are related to the rapid approach to equilibrium, which depends on the sum (A 34[C2H4] -I- k 34), followed by the slower diffusive loss of the equilibrated species from the observation region. Analysis of such data leads directly to third law determinations with the advantage of reduced systematic errors as only one experimental technique is used [71, 72]. 

Other chemical systems can also be utilized to determine AfH (R), probably the most well documented is the hydrogen halide equilibrium  

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