Reactivity Network

The idea for the REACTIVITY NETWORK(2) began as early as 1978 at an international conference on introductory chemistry entitled "New Directions in the Chemistry Curriculum"(t) held at McMaster University. Participants in this Conference agreed that the general chemistry courses at both the high school and college levels are overloaded with theory. Worse still, this oversimplified theory is presented to an audience insufficiently mature to... 

The REACTIVITY NETWORK, directed by E. K. Mellon, began formally in early 1987 with a planning conference supported by the ACS Society Committee on Education. Support for this project by the NSF began in the summer of 1987. The NETWORK is dedicated to reducing the endless mass of inorganic chemical reactivity information in the chemical literature into a form usable by teachers, curriculum developers, and textbook authors. Inorganic chemical reactivity was chosen as the primary focus of the REACTIVITY NETWORK because it provides colorful, interesting phenomena with which to rivet student interest, and because it yields a rich bounty of experimental problems at all levels for students to solve. 

Specifically, Science For All Americans(6 reminds us that what the lecturer projects is not necessarily what the student learns. Meaning must be constructed in the mind by each student individually. Frequently, students must radically restructure thinWng to banish misconceptions. This process requires working with concepts over time in a variety of situations, preferably problem solving ones. The REACTIVITY NETWORK reviews will collect descriptions of chemical phenomena and suggest how the phenomena might be transformed into experimental problems. 

Everyday common sense leads one to the conclusion that laboratory instruction should be dedicated in large part to the solution of experimental problems. Before true problems can be addressed, however, the interest of the student (and often, of the teacher) must be captured. The chemistry sets which made chemistry so attractive to youngsters in years past are now history. The REACTIVITY NETWORK Project will reintroduce many of those engaging chemical phenomena. 

Here are some interest capturers collected from the REACTIVITY NETWORK. The supplies are readily accessible and the procedures simple. Most chemists will be unable to resist trying them ... 

Hybrid materials can be formed when the reaction starts with a functionalized precursor where the fimctionality can either be reactive (a network former) or non-reactive (network modifier). An extensive study used one pulse Si MAS NMR to compare a range of samples with different functionalization. This data, combined with heteronuclear correlation and CP, was able to distinguish materials that were homogeneous or phase separated. As the chain length of the appended organic groups increased there was a decrease in the connectivity of the T-silicons due to steric effects (Peeters et al., 1995). 

More important, tire surface curvature of tire carbon network exerts a profound impact on tire reactivity of tire fullerene core [6, 7]. In tliis context, tire most striking consequence emerges from tire pyramidalization of tire individual carbon atoms. Influenced by tire curvature, tire sp hybrids which exist in tmly two-dimensional planar... 

When a model is based on a picture of an interconnected network of pores of finite size, the question arises whether it may be assumed that the composition of the gas in the pores can be represented adequately by a smooth function of position in the medium. This is always true in the dusty gas model, where the solid material is regarded as dispersed on a molecular scale in the gas, but Is by no means necessarily so when the pores are pictured more realistically, and may be long compared with gaseous mean free paths. To see this, consider a reactive catalyst pellet with Long non-branching pores. The composition at a point within a given pore is... 

In order to cute, ie, form three-dimensional network stmctures through chemical changes on polymer systems with it radiation, it is necessary to design a reactive functionaUty within the polymer stmcture so that coupling reactions can take place between the polymer chains as shown ia the foUowiag reaction ... 

Certain polymeric stmctures can also be blended with other coreactive polymers or multifunctional reactive oligomers that affect curing reactions when exposed to ir radiation. These coreactive polymers and cross-linking oligomers undergo condensation or addition reactions, which cause the formation of network stmctures (Table 9) (4,5,47). 

Unfortunately, because self-condensation of silanols on the same silicone can occur almost spontaneously, the reaction of disdanol or trisilanol compounds with telechelic sdanol polymers to form a three-dimensional network is not feasible. Instead, the telechelic polymers react with cross-linkers containing reactive groups such as alkoxysdanes, acyloxysdanes, silicon hydrides, or methylethyloximesilanes, as in the reactions in equations 18—21 (155). 

In certain distribution networks the natural 1 R drop itself may be sufficiently high to cause a dip at the receiving end that is more than required even when the reactive component is fully compensated. Consequently. such a distribution network may have to be operated underutilized or the size of the current-caiTying conductors may have to be increased to redtice the value of R. and hence the content of I R, and thus raise the capacity of the line. It may thus be concluded that... 

In the following we consider the case of i transmission line, 132 kV and above, being more typical and complex for the purpose of reactive control. Based on this, it would be easier to apply appropriate reactive control to a distribution network and large inductive loads such as an arc or induction furnace. 

I Shunt reactors These are provided as shown in Figure 24.23 to compensate for the distributed lumped capacitances, C , on EHV networks and also to limit temporary overvoltages caused during a load rejection, followed by a ground fault or a phase fault within the prescribed steady-state voltage limits, as noted in Table 24.3. They ab.sorb reactive power to offset the charging power demand of EHV lines (Table 24.2, column 9). The selection of a reactor can be made on the basis of the duty it has to perform and the compensation required. Some of the different types of reactors and their characteristics are described in Chapter 27. 

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