Monomolecular Reactions

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Monomolecular Reactions

 

chemical reactions in which a single molecule undergoes transformation in the elementary event. Monomolecular reactions include the numerous decomposition reactions of complex molecules and isomerizations. For example, the decomposition of ethyl chloride

C2H5Cl→C2H4 + HCl

and the isomerization of methyl isonitrile to acetonitrile

CH3NC→CH3CN

are monomolecular reactions.

The rate of monomolecular reactions (in ideal gaseous mixtures and liquid solutions) is described by a first-order kinetic equation r = kc, where r is the rate of reaction, c is the concentration of the initial material, and k is the rate constant (which depends on the temperature according to the Arrhenius equation). At a constant volume, r = −dc/dt, where t is time and c = c0ekt(C0 is the value for c at t = 0).

At reduced pressures, the values of r for gaseous-phase monomolecular reactions are smaller than those expected from the first-order kinetic equation because of an insufficient rate of intermolecular energy transfer as a result of a reduced frequency of molecular collisions.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
where k, A, [E.sub.A], R, and T are the rate constant, pre-exponential factor, activation energy, gas constant, and temperature, respectively, [k.sub.B], h, and [C.sub.TO] are the Boltzmann constant, Planck constant, and total concentration of reactive sites (which should be left out in the case of monomolecular reactions, i.e.