Macroscopic perspective

To visualize how electrochemical cells generate electrical potential differences, consider a zinc electrode dipped into a solution of zinc sulfate. From the macroscopic perspective, nothing happens. At the molecular level, however, some of the zinc atoms of the electrode are oxidized to ions ... 

Figure 19-11 illustrates the zinc equilibrium at the molecular level. At equilibrium, the charge imbalance in the zinc strip is about one excess electron for every 10 zinc atoms. This is negligible from the macroscopic perspective but significant at the molecular level. 

A dislocated crystal has a distinct geometric character from one that is dislocation-free. From both the atomistic and continuum perspectives, the boundary between slipped and unslipped parts of the crystal has a unique signature. Whether we choose to view the material from the detailed atomic-level perspective of the crystal lattice or the macroscopic perspective offered by smeared out displacement fields, this geometric signature is evidenced by the presence of the so-called Burgers vector. After the passage of a lattice dislocation, atoms across the slip plane assume new partnerships. Atoms which were formerly across from... 

Continuum Models of Diffusion and Heat Transport. As seen in chap. 7, the accumulated unbiased hopping of atoms can lead to a macroscopic appearance of design-, namely, that there seems to be a force leading to a preference for motion in a given direction. From a macroscopic perspective, this apparent biased motion of atoms is reflected through the diffusion equation given earlier as eqn (7.18) and which is repeated here for ease of discussion as... 

Harmonic Oscillators and Optical Absorption. An ingenious example of exploiting insights at one scale in order to inform those at another is that of optical absorption in solids. From a macroscopic perspective, the attempt to understand absorption is founded on Maxwell s theory of the electromagnetic field. However, in order to make material specific progress, it is necessary to supplement these ideas with either a phenomenological or microscopic model of material response. 

Observations of the composition and behavior of matter are based on a macroscopic view. Matter that is large enough to be seen is called macroscopic, so all of your observations in chemistry, and everywhere else, start from this perspective. The macroscopic world is the one you touch, feel, smell, taste, and see. The properties of iron shown in Figure 1.3 are seen from a macroscopic perspective. But if you want to describe and understand the structure of iron, you must use a different perspective—one that allows you to see what can t be seen. What you can see of the New York City World Trade Center, shown in Figure 1.5, is similar to a macroscopic perspective. The actual structure of the building is hidden from view. 

In the next two sections, we review some recent work that addresses, at the molecular level, the nature of the main parameters that govern electron-transfer processes in tr-conjugated oligomers and polymers. This molecular approach contrasts with many models developed earlier for organic materials (where these processes were described on a phenomenological basis) and from a macroscopic perspective, thereby masking the actual chemical structures of the systems behind effective parameters. 

This partial differential equation is often called the Fokker-Planck equation. The great benefit of the Fokker-Planck equation is that it enables the macroscopic perspective on the solutions of an SDE. 

The Study of Chemistry The Macroscopic Perspective The Microscopic or Particulate... 

This coherent picture involves three levels of understanding or perspectives on the nature of chemistry macroscopic, microscopic, and symbolic. By the end of this course, you should be able to switch among these perspectives to look at problems involving chemistry in several ways. The things we can see about substances and their reactions provide the macroscopic perspective. We need to interpret these events considering the microscopic (or particulate ) perspective, where we focus on the smallest components of the system. Finally, we need to be able to communicate these concepts efficiendy, so chemists have devised a symbolic perspective that allows us to do that. We can look at these three aspects of chemistry first, to provide a reference for framing our studies at the outset. 

We call this a dynamic equilibrium because the evaporation and condensation do not stop at equilibrium. The rates of these competing processes become equal to one another, but they do not go to zero. So on the microscopic level, individual molecules continue to move from the liquid to the vapor phase and back again. But from a macroscopic perspective, the observable amounts of liquid and vapor no longer change. 

The waU of a cellulose fiber in turn exhibits a complex, laminar structure, wherein each layer consists of smaller, unidirectional fibers, or microfibrils, in the range of 5 to 50 run wide, and anywhere from 100 run to several microns long, depending on the source [33]. Each layer of microfibrils varies with respect to fibril orientation (microfibril angle). Microfibrils in turn have a composite stracture, consisting of slender cellulose crystallites, or whiskers, with diameters on the order of 5 run, which are threaded together and embedded in the microfibrils between amorphous regions of cellulose and hemicellulose [34]. Hence, cellulose can be viewed as a composite material from the nanoscale perspective (whiskers in microfibrils), the microscopic perspective (microfibrils in fibers), and the macroscopic perspective (fibers in wood). 

For illustrative purposes, to demonstrate the state of polyolefin recycling in 1992, the life of 200 kg of virgin HOPE bottle resin is studied. The assumptions are that 10% of the resin is used in milk bottles, which is a homopolymer product, 8% is used in motor oil bottles, a difficult to clean product, and the remainder is used in other consumer bottles. A macroscopic perspective suggests that consumer products use about 5% post consumer recycled material and motor oil bottles about 25%. Some products would use more and some none at all. This does not take post industrial or internal scrap levels into consideration in terms of reclaimed content. It can be concluded that, at the current levels of recycling, a large fraction of the polyolefin molecules will be exposed to at most 4 thermal and shearing cycles. 

We are grateful for all the hard and time-consuming work that the symposium lecturers and poster contributors devoted to this meeting. Also, we are espeically appreciative of the efforts of the many authors who provided written chapters comprising this volume, and of the reviewers for their comments. The willing participation of researchers from a broad cross-section of science and engineering disciplines, especially those from the more macroscopic perspective, was essential to the success of such a meeting, and provided the necessary framework upon which discussions were built. 

From a macroscopic perspective, almost all the water-soluble films are hydrophilic materials. There is a large number of hydrophilic polar group in the molecular structure. The dissolution mechanism of water-soluble PVA film can be explained as follows PVA absorbs large amounts of water molecules and in order to make the molecules expand and resolve, the temperature is raised with continued heating. Then the numerous molecules which are made of carbon, oxygen, and hydrogen, are resolved into CO2 and H2O. And CO2 ultimately evaporates into air. It explains the fact that hydrolysis products of PVA do not harm the environment and they are environment-friendly materials. 

From a macroscopic perspective, a chemical reaction consists of a vast amount of sequential, individual, chemical steps. Each step takes place when one or more molecules of one or more chemical species (the reactants) interact via collisions and transform their chemical nature to give rise to a different set of molecules of distinct chemical species (the products). Strictly speaking, all chemical reactions are reversible because it is possible that the product molecules collide in such a way that they react and give rise to the reactant molecules. The usual way to represent these processes is as follows ... 

Interdiffusion may be discerned from a macroscopic perspective by changes in concentration that occur over time, as in the example for the Cu-Ni diffusion couple. There is a net drift or transport of atoms from high- to low-concentration regions. Diffusion also occurs for pure metals, but all atoms exchanging positions are of the same type this is termed self-diffusion. Of course, self-diffusion is not normally subject to observation by noting compositional changes. 

From the macroscopic perspective, matter is continuous rather than composed of discrete particles. As already noted, this is expressed in the application of mathematical analysis in thermodynamics and its extensions. This conception of matter is reflected here in the distributive condition, which goes back to Aristotle who took a definite stand against the discrete, atomic conception of matter. This stand might seem anachronistic today. But classical atomism of the crude kind opposed within an Aristotelian tradition up to the end of the 19th century is not what modern theories based on quantmn mechanics support. And notions of same substance still derive, as we saw, from macroscopic theory. But there is an objection to the distributive condition which doesn t hinge on appeal to parts of water smaller than the smallest part which is water and raises the issue of the nature of mixture. 

Pressure (P) Pressure is similar to temperature in that, from a macroscopic perspective, there is no physical meaning for pressure of an individual molecule. For a continuous mixture, pressure is a measure of the molecular momentum transfer from collision on the plane of measurement. Consider a balloon filled with helium, as in Figure 3.2. To expand the balloon against the restraining force of the elastic balloon material, there must be an internal pressure greater than the atmospheric pressure. At the balloon s internal surface, the molecules are colliding and refiecting off of the wall. Since the internal pressure must... 

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