Conceptual and Quantitative Questions

Interfacial mass transfer. Although mass transfer inside the bulk of a solid or fluid phase is of interest and application in chemical and bioprocesses, the mass transfer across interphases is of special interest in the discipline. As example when brewing tea, there is a diffusion process inside of the tea leaves of the molecules responsible for tea flavor and color. Then there is mass transfer (due to diffusion, convection and dispersion) of these molecules to the water in the bulk of the cup. 

However is in the interphase of the systems, the boundary between the tea leaves and the water, where more resistance to mass transfer occurs. This interphase mass transfer is usually a combination of different mechanisms. Most of the time this resistance to mass transfer is difficult to calculate but can be estimated using empirical and semi-empirical observations. 

similarly to heat transfer, this resistance to mass transfer is modeled using a mass transfer coefficient (analogous to the heat transfer coefficient defined earlier)  

As stated at the beginning, all the concepts required in the solved- and proposed-problem sections were learned (or should have been learned) in high school. Assuming that it is necessary to review certain concepts, we will take the opportunity to do an exhaustive review in the solved-problem section. Some of the concepts to be reviewed include, for example, ideal gas mixtures, Dalton s law, and Amagat s law. But we will also keep it simple the focus will be, as in previous chapters, on tackling problem formulation  

As you will see, most of the quantitative problems in the following sections are concern ideal gases and just a glimpse of material balance. The next chapter is devoted entirely to material balance. Here, the introductory parts on thermodynamics, heat transfer, and mass transfer were included to acquaint you with the chemical and bioprocess engineering world conceptually, but not quantitatively. 

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This collection of worksheets (about three per chapter) is for students to use in collaborative groups. Designed to stimulate group activity and discussion, the questions provided on each worksheet are equally conceptually and quantitatively oriented. Also included are instructions for use, information on how to guide student discussion, and supporting data on the success of cooperative learning at the University of Connecticut... 

The interfacial aqueous coordination chemistry of natural particles, in particular their surface complexation reactions, owes much of its development to the research of Werner Stumm. Beginning with the tentative interpretation of specific adsorption processes in terms of chemical reactions to form inner-sphere surface complexes, his seminal questions spawned a generation of research on the detection and quantitation of these surface species. The application of noninvasive spectroscopy in this research is exemplified by electron spin resonance and extended X-ray absorption fine structure studies. These studies, in turn, indicate the existence of a rich variety of surface species that transcend the isolated surface complex in both structure and reactivity, thereby stimulating future research in molecular conceptualizations of the particle-water interface. 

For a non-science majors course, the traditional textbook sequencing of topics was simply too prolonged to prepare students within one semester to pursue independent research and answer quantitative questions on chemical issues. Building guided-inquiry activities for this course had been defined by the need to reach specific conceptual levels such as redox reactions and stoichiometry as early as possible. To accomplish these objectives chemical topics were reordered, simplified and conceptually integrated. Furthermore, to address the challenge of conceptually... 

Sawrey (1990) repeated the work by Nurrenbern and Pickering with a larger, more uniform group of students. She compared success on conceptual versus numerical problems for students in the top and bottom of the class, to see if the effect disappears for higher achievers. Even the best numerical problem solvers, however, performed poorly on the conceptual questions. She argued that the qualitative, conceptual side of chemistry has suffered as a consequence of the emphasis in recent years on quantitative problems and argued for simultaneously giving attention to both the qualitative and quantitative nature of chemistry. 

Shewhart s basic conceptualization of common and special cause variation not only leads to control charts as quantitative, rational tools to guide one in knowing when (and when not ) to intervene in an industrial process to correct potential ills, but it also provides a framework for considering the question of what is the best/most consistent performance one can hope for from a particular version of a process. That is, it provides a framework for discussing process capability assessment. 

Hansch QSAR and related approaches belong to the world of numbers conceptually, knowledge-based expert system approaches do not. Three areas of debate about expert systems have arisen from the distinction. Can you devise ways to generate qualified output from computer-based expert systems without hiding quantitative methods inside them Assuming you can, how do you validate an expert system How can you usefully combine output from different systems—some quantitative and some qualitative—to make predictions more reliable The first of the questions is more a historical than a current one some of the systems described earlier in this chapter demonstrate... 

Intertidal areas are difficult to study from a practical point of view and offer conceptual challenges to developing the quantitative budgets required to address questions about nutrient transport between land and sea. The methods employed must take account of the key attributes of the intertidal environment which include variability, patchiness scales and... 

Nurrenbern Pickering (1987) proposed an alternative to the quantitative approach to teaching chemistry that had become the accepted one. In their study, students were asked to do both a traditional problem on gases and a multiple-choice queshon that had no mathematical content but asked for a purely conceptual understanding of gases. They found that the students had far greater success answering the traditional questions than the conceptual questions. 

A conceptually different and relatively new example of an inferential model, motivated by human performance problems specifically, is nonlinear causal resource analysis (NCRA) [Kondraske, 1988 Vasta and Kondraske, 1994]. Quantitative task demands, in terms of performance variables that characterize the involved subsystems, are inferred from a population data set that includes measures of subsystem performance resource availabilities (e.g., speed, accuracy, etc.) and overall performance on the task in question. This method is based on the following simple concept Consider a sample of 100 people, each with a known amount of cash (e.g., a fairly even distribution from 0 to 10,000). Each person is asked to try to purchase a specific computer, the cost of which is unknown. In the subgroup that was able to make the purchase (some would not have enough cash), the individual who had the least amount of cash provides the key clue. That amount of cash availability provides an estimate of the computer s cost (i.e., the unknown value). Thus, in human performance, demand is inferred from resource availabdities. 

From a conceptual point of view, this technical problem is related to a qualitative question would it be possible to define a universal monoelectronic potential characteristic of an atom, say the C atom Any chemist would consider that atoms in molecules keep some of the characteristics of the isolated atoms. Is it possible to give a quantitative justification of this idea It would be interesting, for instance, to estimate whether singly, doubly and triply bonded carbon atoms can be considered as fixed carbon atoms in the series of saturated and conjugated hydrocarbons. It will be shown below that quantum chemistry is able to determine purely monoelectronic (pseudo)potentials of atoms in molecules and to check their transferability. 

Our thesis is that there is a severe mismatch between the way people come naturally to view and understand the world, and the forms of physical theories with which they are presented in textbooks and classrooms. We are interested in mismatches between students ways of reasoning about the physical world and the types of reasoning embodied in the physics curriculum. We shall also argue that physical theories - presented solely as abstract, mathematical models - do not do justice to the multiple types and levels of conceptualization that expert users of physics have built over years of experience with the subject. So the question becomes What are the mismatches in form and content between the conceptual models of "textbook physics" and those of naive students of physics What clues to more profitable ways of modelling physical systems can be found in the reasoning of expert practitioners of physics/engineering And finally, how can we assist students in the construction of mental mc els of physical systems that will support a deep understanding of physical mechanisms from both a qualitative and a quantitative standpoint ... 

However there are many questions that arise about these properties of evidence and in particular how we measure them either qualitatively or quantitatively. Currently, a large amount of the consideration of relevance occurs on a case-by-case basis using subjective judgement. Conceptual frameworks for assessing relevance, trustworthiness and independence methodically and the presentation of this information in the safety case would improve our understanding of the role the evidence plays. This problem is not specific to goal-based standards and is equally applicable to evidence generated to satisfy prescriptive standards. 

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