This Text

We do not feel that it is possible (for us), or perhaps even desirable, to present the study of biogeochemistry in the form of a series of recipes or a dogma that can be plugged into any new biogeochemical problem. We do hope to identify some of the key elements common to the study of many of these systems. We offer a variety of approaches to the problems and offer a framework within which one may critically examine any study of biogeochemistry. Finally, we hope to encourage a spirit of experimentation in the development of new ways of looking at these complex systems. 

Let us briefly consider a system that will have little practical value other than to serve as a basis from which we can describe the organization of the book. The description of the Earth as a system may be undertaken by defining the biological, chemical, and physical states of all of its parts as well as the positions and kinetic energies of these parts. 

Points within this many-dimensional system are defined by a location variable (denoted by X) a chemical state variable (Q, and biological and physical state variables (B and P). To complete the description of the system, the densities or concentrations near a point, N X,C,B,P), will be required. These functions will in general be time-dependent. Although we might think of this system as a cube, it should actually be represented as an n- space and not bound in the sense implied by the cube. Further notes on the variables follow. 

The location variables (x, y, and 2 in a Cartesian coordinate system) vary continuously. We may, however, choose to study a selected domain for example, allow x, y, and 2 range so as to include only the oceans or only a particular estuary. The location variable may also be chosen to range only over a space that is homogeneous with respect to density or concentration. This would be the beginning of a box model (described in Chapter 4). 

The physical relationships of various regions of the system and the transfer processes must also be defined. This will include a description of the important chemical reactions and their rate constants, dispersion and transport processes, and the fact that sediments and the oceans share a surface. The internal structure can be complex. For example, the population of kelp in a portion of the ocean can be coupled to the population of sea otters through the harvesting of kelp by the sea urchins and predation of sea urchins by sea otters. Exogenous inputs and outputs such as the influx of solar radiation and meteoritic matter and the efflux of infrared radiation, helium, and hydrogen are obvious examples when the system represents the entire Earth. 

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This text will attempt to develop an understanding of the concepts required at each stage during the creation of a chemical process design. 

Later in this text an approach is presented in which some early decisions (i.e., decisions regarding reactor and separator options) can be evaluated without a complete design for the outer layers. ... 

Now we consider some of the methods by which such separations can be achieved. A comprehensive survey is beyond the scope of this text, and many good surveys are already available. ... 

As the design progresses, it is necessary to carry out hazard and operability studies. These are generally only meaningful when the design has been progressed as far as the preparation of detailed flowsheets and are outside the scope of this text. 

There are many other sources of waste associated with process operations which can only be taken care of in the later stages of design or after the plant has been built and has become operational. For example, poor operating practice can mean that the process operates under conditions for which it was not designed, leading to waste. Such problems might be solved by an increased level of automation or better management of the process. These considerations are outside the scope of this text. 

They are classified apart in this text because their use differs from that of petroleum solvents they are used as raw materials for petrochemicals, particularly as feeds to steam crackers. Naphthas are thus industrial intermediates and not consumer products. Consequently, naphthas are not subject to governmental specifications, but only to commercial specifications that are re-negotiated for each contract. Nevertheless, naphthas are in a relatively homogeneous class and represent a large enough tonnage so that the best known properties to be highlighted here. 

Expectation curves are alternatively known as probability curves . This text will use the term expectation curve for conciseness. 

A case can be made for the usefulness of surface tension as a concept even in the case of a normal liquid-vapor interface. A discussion of this appears in papers by Brown [33] and Gurney [34]. The informal practice of using surface tension and surface free energy interchangeably will be followed in this text. 

A relatively complete survey of quantum chemistry, written on a level just below that of the Szabo and Ostiund text. Levine has done an excellent job in including up-to-date material in successive editions of this text, which makes for interesting as well as informative reading. 

This text covers quantitative analysis by electron energy-loss spectroscopy in the electron microscope along with instrumentation and applicable electron-scattering theory. 

There are 42 Computer Projeets ineluded in this text. Several of the Computer Projeets eonneet with the researeh literature and lead to extensions suitable for undergraduate or MS thesis projeets. All of the eomputer projeets in this book have been sueeessfully run by the author. Unfortunately, we still live in an era of system ineompatibility. The instiuetor using these projeets in a teaehing laboratory is urged... 

This text is intended for use by beginning graduate students and advaneed upper division undergraduate students in all areas of ehemistry. 

To provide a text that students ean use to gain introduetory level knowledge of quantum meehanies as applied to ehemistry problems, sueh a non-historieal approaeh had to be followed. This text immediately exposes the reader to the maehinery of quantum meehanies. 

It is antieipated that a eourse dealing with atomie and moleeular speetroseopy will follow the student s mastery of the material eovered in Seetions 1-4. For this reason, beyond these introduetory seetions, this text s emphasis is plaeed on eleetronie stmeture applieations rather than on vibrational and rotational energy levels, whieh are traditionally eovered in eonsiderable detail in speetroseopy eourses. 

To further assist the learning proeess, readers may find it useful to eonsult other textbooks or literature referenees. Several partieular texts are reeommended for additional reading, further details, or simply an alternative point of view. They inelude the following (in eaeh ease, the abbreviated name used in this text is given following the proper referenee) ... 

In cases where the elassieal energy, and henee the quantum Hamiltonian, do not eontain terms that are explieitly time dependent (e.g., interaetions with time varying external eleetrie or magnetie fields would add to the above elassieal energy expression time dependent terms diseussed later in this text), the separations of variables teehniques ean be used to reduee the Sehrodinger equation to a time-independent equation. 

The full N-eleetron non-relativistie Hamiltonian H diseussed earlier in this text involves the kinetie energies of the eleetrons and of the nuelei and the mutual eoulombie interaetions among these partieles... 

It turns out (the development of this eoneept is beyond the seope of this text) that the rate at whieh an exeited level ean emit photons and deeay to a lower energy level is dependent on two faetors (i) the rate of stimulated photon emission as eovered above, and (ii) the rate of spontaneous photon emission. The former rate gf Ri,f (per moleeule) is proportional to the light intensity g(cofj) at the resonanee frequeney. It is eonventional to... 

Ei=i N F(i), perturbation theory (see Appendix D for an introduetion to time-independent perturbation theory) is used to determine the Ci amplitudes for the CSFs. The MPPT proeedure is also referred to as the many-body perturbation theory (MBPT) method. The two names arose beeause two different sehools of physies and ehemistry developed them for somewhat different applieations. Later, workers realized that they were identieal in their working equations when the UHF H is employed as the unperturbed Hamiltonian. In this text, we will therefore refer to this approaeh as MPPT/MBPT. 

Most of the modeling methods discussed in this text model gas-phase molecular behavior, in which it is reasonable to assume that there is no interaction with other molecules. However, most laboratory chemistry is done in solution where the interaction between the species of interest and the solvent is not negligible. 

Of all the topics discussed in this text, mesoscale simulations are probably at the most infantile stage of development. The idea of the mesoscale calculations is very attractive and physically reasonable. However, it is not as simple as one might expect. The choice of bead sizes and parameters is crucial to obtaining physically relevant results. More complex bead shapes are expected to be incorporated in future versions of these techniques. When using one simulation technique to derive parameters for another simulation, very small errors in a low-level calculation could result in large errors in the final stages. 

All of the material in this text and most of chemistry generally can be understood on the basis of what physicists call the electromagnetic force Its major principle is that opposite charges attract and like charges repel As you learn organic chemistry a good way to start to connect structure to properties such as chemical reactivity is to find the positive part of one molecule and the neg ative part of another Most of the time these will be the reactive sites... 

Like nitric acid each of the following inorganic compounds will be frequently encountered in this text Calculate the formal charge on each of the atoms in the Lewis structures given... 

It IS good chemical practice to represent molecules by their most stable Lewis structure The ability to write alternative resonance forms and to compare their relative stabilities however can provide insight into both molecular structure and chemical behavior This will become particularly apparent m the last two thirds of this text where the resonance concept will be used regularly... 

Accompanying this text is a CD entitled Learning By Modeling As its name implies it is a learning tool designed to help you better understand molecular structure and properties and contains two major components... 

SpartanBuild software that you can use to build molecular models of various types include tube ball and spoke and space filling This text includes a number of mod eling exercises for you to do but don t limit yourself to them You can learn a lot by sim ply experimenting with SpartanBuild to see what you can make... 

SpartanView software with which you can browse through an archive of already prepared models on the Learning By Modeling CD These models include many of the same substances that appear m this text SpartanView is the tool you will use to view... 

Immediately preceding the Glossary at the back of this text IS a tutorial showing you how to use Spar-tanBuild and SpartanView and describing some addi tional features... 

As you go through this text you will see two dif ferent modeling icons The SpartanBuild icon alerts you to a model building opportunity the SpartanView icon indicates that the Learning By Modeling CD includes a related model or animation... 

Section 1 1 A review of some fundamental knowledge about atoms and electrons leads to a discussion of wave functions, orbitals, and the electron con figurations of atoms Neutral atoms have as many electrons as the num ber of protons m the nucleus These electrons occupy orbitals m order of increasing energy with no more than two electrons m any one orbital The most frequently encountered atomic orbitals m this text are s orbitals (spherically symmetrical) and p orbitals ( dumbbell shaped)... 

Each of the following species will be encountered at some point in this text They all have the same number of electrons binding the same number of atoms and the same arrangement of bonds they are isoelectromc Specify which atoms if any bear a formal charge in the Lewis stmc ture given and the net charge for each species... 

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