Ice cubes, held in a flow of water maintained at a constant temperature, me
lt at a rate that is well expressed by the contracting volume rate equation
, familiar from kinetic studies of solid state reactions. The apparent acti
vation energy, 28.5 +/- 3.0 kJ mol(-1) between 276.2 and 303.4 K, is close
to the strength of the hydrogen bond in ice. From these observations, it ap
pears that this physical change exhibits a pattern of kinetic features that
is superficially identical with behavior characteristic of the chemical st
eps occurring during thermal decompositions of solids. However, careful exa
mination of the rate data at the temperatures closest to the melting point
of ice shows that here rates are much slower than is consistent with expect
ation from the Arrhenius line. It is concluded, therefore. that rate consta
nt measurements are more satisfactorily represented overall by a rate of in
terface advance, during fusion, that is directly proportional to heat how:
this is directly proportional to the difference between the temperatures of
the ice surface and of the flowing water. It follows that the melting rate
is most satisfactorily represented as being controlled by heat transfer ac
ross a boundary layer of moving liquid, close to the ice surface. These alt
ernative analyses of the same data are presented to emphasize that mechanis
tic and kinetic interpretations of rate processes involving solids must be
based on realistic assessments of conditions within the zone of change. Thi
s demonstration that a kinetic expression that is characteristic of solid s
tate reactions satisfactorily describes the data together with an activatio
n energy that correlates with a known bond strength in the reactant does no
t necessarily prove that a solid state, activated reaction is occurring her
e. Aspects of the mechanistic interpretations of the kinetic characteristic
s of many solid state decompositions remain difficult to understand and are
incompletely resolved. (C) 2001 Elsevier Science B.V. All rights reserved.