I&EC REPORTS & COMMENTS British scheme for chemical engineering education Relative chemical activities of halides determined New view of thermal equilibrium
British Course in Chemical Engineering With the current attention being given in the U. S. to the controversial ASEE report on the Goals o i Engineering Education, it is appropriate that the Institution of Chemical Engineers in Great Britain should choose this moment to reissue their booklet, “Scheme for a Degree Course in Chemical Engineering.” In a concise and direct manner, the Institution outlines an undergraduate curriculum that it feels would be a desirable model for most British colleges and univenities. Although not intended to dictate course requirements to any academic body, the scheme does specify the ingredients which satisfy the examination requirements for entry into IChE. The British program amumes that students begin their training after graduating from a secondary school a t the advanced level. I t also assumes that the full time student will complete the course in three years, including summer employment in industry. With the 5-year curriculum already in existence in several U. S. universities, this would appear to be a strenuous, alKit a refreshing, reversal of the American trend. Several reasons for the adequacy of a three-year course become apparent from a glance at the course subject outlined at right. There is immediate, if minor, specialization by dividing the course into two options: a design option and a process option. Although selected upon entry into the university, the options are sufficiently flexible to allow the student to change within a reasonable period of time after beginning his study. This effectively &nates the need for the first year of general training that is common in the United States and is aimed at allowing the student to orient himself sufficiently to make a reasonable choice.
The British course does not contain the “humanities” electives that are common in the United States. Further, the British students apparently have no formal requirement for ROTC or other military training. Despite its lean appearance, the British course rdects the current trend toward accenting fundamental scientific principles rather than descriptive treatment. At the same time, there is considerable work on sketching and engineering drawing,
items which have been discarded from most U.S. courses. The Engineering Laboratories suggested by the Institute correspond, in general, to U. S. belidsthatbench scale equipment should replace the familiar unit operations laboratory. Even so, there is still room for exposure to process equipment through the expected summer employment in industry. (Continued on jug8 76) VOL 5 8
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I&EC REPORTS
SUPERFINE GRINDING
It would probably be a mistake for the Institution’s course to be considered for adoption in the United States. Nonetheless, the course does refocus our attention on the traditional reason for engineering education-to prepare students for industrial engineering careers by providing them with knowledge and the “engineering approach” to its use.
Chemical Activities of Halides The relative chemical activities of solid and molten halides have been established by W. J. Hamer at the Institute for Basic Stand1
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INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
ards of the National Bureau of Standards. The series are based on the free energies of formation of the electrolyte phase and the heat capacities of the elements (electrodes) in the electrolyte phase. Series have also been prepared for the range 25” to 3000’ C. Elements are arranged according to their reducing power but the order differs in the several series. Lithium metal, for example, if placed in molten barium fluoride, would displace the barium with the formation of lithium fluoride. In molten bromides, however, the reverse occurs. The series for bromides and chlorides at 25’ C, is shown below.
TABULATION OF RELATIVE CHEMICAL ACTIVITIES OF HALIDES*
Thermal Equilibrium Reconsidered For any thermodynamic system in thermal equilibrium, the temperature of the system must be uniform and constant. Additional conditions are commonly assumed. However, the additional conditions may not be valid, making temperature alone an inadequate criterion. Professor M. A. Melehy of the University of Connecticut has considered the characterization of thermal equilibrium [Nuture 209, 670 (Feb. 12, 1966)] and concluded that greater care must be exercised in specifying thermal equilibrium. We note that, with the growing interest in mechanistics, his remarks are pertinent to a number of problems in thermodynamic analysis encountered by industrial chemists and engineers. I t is generally assumed that, for systems in thermal equilibrium, the chemical potential is constant throughout. Similarly, it is also frequently assumed-for example, across a vapor liquid interface-that the Gibbs function (C) is also invariant. Prof. Melehy objects to this assumption because dp # 0 and because assuming dP = 0 contradicts the virial theorem. Prof. Melehy distinguishes between the conventional conception of ‘(external pressure” and “internal pressure,” which describes an inaccessible physical quantity much like internal energy. Despite its inaccessibility, the internal pressure of a liquid would be responsible for the transport of particles. With these objections to conventional criteria for thermal equilibrium in mind, Prof. Melehy formulates new criteria. He shows that generally the differentials of the chemical potential, the Helmholtz free energy, and the Gibbs free energy must all become exact rather than vanish as is conventionally assumed. These criteria result from a set of generalized transport laws
formulated to describe steady-state conditions associated with timeindependent processes. Central to these generalized transport laws is the development of a thermodynamic force. In problems involving the transport of mobile particles, it is convenient to think in terms of the average work done on, rather than done by, a transported particle. Prof. Melehy thus defines a quantity v at any point A within a small volume V enclosing N particles to be the average work done on each particle transported from some reference point along a prescribed path to A . The transport is the result of purely thermodynamic processes. He shows that AY = S A T - ( l / n ) V P and, since v has the dimension of
energy, V v has the dimension of force denoted by fc. Each of the other terms in the equation must also be a force (dimensional homogeneity), and we may rewrite the equation as ft
= fT $. fd
i.e., the thermodynamic force is the sum of a thermal force f r resulting from a temperature gradient and a diffusion force fd which is mechanical and results from a pressure gradient. It is clear, therefore, that the existence of fd automatically requires that dP = 0, in addition to d T = 0, before thermal equilibrium can be assumed. Although Prof. Melehy habitually uses the transport of electrons in solids as an example, he explicitly generalizes the results to apply to mobile particles in closed systems.
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