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<br />21
<br />
<br />tests in the 'dynamio' cloud chamber at CSU. More ioe orystals appeared
<br />at a faster rate when an initially dry (-300C dewpoint), room
<br />
<br />temperature sample was injeoted into a cold. cloudy euvironment than
<br />
<br />when a similar sample was injected into a warmer, subsaturated
<br />
<br />environment.
<br />
<br />2.2 Chemical Kinetio Methodoloav in the Study of Phase Chanae
<br />
<br />The inoorJ?9ration of chemical kinetic _thodology 1,.n 1;.i!!. s1;.\1~f
<br />heterogeneous ice nuoleation has been introduced only recently. (DeMott,
<br />
<br />_.._....."~,,,."~-_.._.._..~,,....., -~,~.,....._.,...:.._=-..... .
<br />
<br />1'82, DeMott, et al., 1'83, and Reiss, 1'82). The theraodynamio
<br />
<br />.........---.-. '-- .~---..,,~ _.,,,,"'-"'''''-~-"-..--
<br />
<br />approaoh to ice nu~~eation research, oftel1_~r~!z:-red to as the ' classioal
<br />~:>.::"9~...."...,..,...---_.... .'-'~~N">"~__","",.._____"_,~
<br />
<br />model' (Turnbull and Vonnegut, 1'52, Fletcher, 1'58, 1'59, 1968, 1'6',
<br />
<br />~"-'''.'''~~~''''~_'_'_~.V'''
<br />
<br />Fukuta and Schaller, 1'82, Pruppacher and nett, 1978, p. 268-281) ,__1188_
<br />
<br />received the most attention. These two approaches ditfer markedly in
<br />
<br />their respective starting assumptions and lines of reasoning. Certain
<br />
<br />___~_~'__ ,__'_'_~ -"c,~"",~,_,,'____:'__,"'~~'~" ".'
<br />
<br />properties, most i.portantl~_..tbe teJII~oral nat\lr_~._,~~ the physioal process
<br />of phase change, can be determined only via chemical kinetios and not by
<br />
<br />a ther.odYnam~~~~!pproaoh.
<br />General prinoiples of chemical kinetics as an emperical diScipline
<br />can be found in most textbooks of physical ohemistry (eg. Moore, 1972,
<br />
<br />and Berry, et al., 1'80). Chemical kinetics addresses the evolution in
<br />
<br />time of a chemioal or physioal prooess or reaction. It is based on the
<br />,'.--,..."'-... -:t -_._-~~--'--'--"- -.--
<br />
<br />Law of Mass Aotion which states that the dynamic rate of a reaction or
<br />
<br />
<br />-..--~'-"~~ .--.,.~------~---~..--'
<br />
<br />An example
<br />
<br />
<br />process is dependent on the concentration of the reactants.
<br />
<br />of the information ldnetics provides about phase change in a ChemiCally
<br />homogeneous system is given in Berry, et ale (1'80, p. 1025). . Water in
<br />
<br />a oontainer open to the atmosphere will evaporate. Changes in
<br />
<br />thermodynamic state functions depend only on the initial and final
<br />
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