Volume Profile of the Reversible Dimerization Reaction of 2‐Methyl‐2‐nitrosopropane: Validity of the Hard Sphere Fluid Model and the Transition State Theory

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Abstract
The volume profile of the reversible dimerization reaction of 2‐methyl‐2‐nitrosopropane in carbon tetrachloride was determined at 25.0°C on the basis of the study of the pressure effect and the measurement of the solution density at 0.1 MPa. For the dissociation process, the configurational reaction volume was +30.3 ± 0.8 cm3 mol−1 and the apparent activation volume was +7.7 ± 0.3 cm3 mol−1 at 25.0°C and 61.3 MPa. The configurational reaction volume at 0.1 MPa was estimated as +36 cm3 mol−1 from the high pressure study in agreement with the result of the density measurement. The experimental values of the reaction and activation volumes were successfully reproduced by using the hard sphere fluid model. The agreement of experiment and theory indicates that the hard sphere fluid model is valid for describing the volume change for the molecular reaction, and implies that the transition state theory (TST) is valid for interpreting the pressure dependence of the rate constant. A simple illustration of the validity of TST is presented; the energy relaxation process plays a key role in determining the validity.