Reality, meaning

In the discussion of dicomplex systems we do not begin with the apparently simplest case — the limiting case No. 7 — and by gradually replacing a microion by a colloid ion (No. 5 or 6) finally arrive at the apparently complicated case No. 4 where both ions are colloid ions. Such a treatment is certainly not the way because, going from No. 7 via No. 5 and 6 to No. 4 does not in reality mean a complication but rather a simplification. 

It is useful, nevertheless, to bring to mind their composition and their means of action (Goodacre, 1958). Several components of the same family can in reality be utilized tetraethyl lead, Pb ( 2115)4 or TEL, tetramethyl lead, Pb (CHg) or TML, mixtures of these products or yet mixed chemical components including various combinations of the groups C2Hg and CH3 Pb ( 2115)2 ( 113)2, Pb ( 2115)3 113, Pb ( 2Hg) ( 113)3. 

By expressing the mean-field interaction of an electron at r with the N- 1 other electrons in temis of a probability density pyy r ) that is independent of the fact that another electron resides at r, the mean-field models ignore spatial correlations among the electrons. In reality, as shown in figure B3.T5 the conditional probability density for finding one ofA - 1 electrons at r, given that one electron is at r depends on r. The absence of a spatial correlation is a direct consequence of the spin-orbital product nature of the mean-field wavefiinctions... 

This discussion may well leave one wondering what role reality plays in computation chemistry. Only some things are known exactly. For example, the quantum mechanical description of the hydrogen atom matches the observed spectrum as accurately as any experiment ever done. If an approximation is used, one must ask how accurate an answer should be. Computations of the energetics of molecules and reactions often attempt to attain what is called chemical accuracy, meaning an error of less than about 1 kcal/mol. This is suf-hcient to describe van der Waals interactions, the weakest interaction considered to affect most chemistry. Most chemists have no use for answers more accurate than this. 

We can consider the hydroboration step as though it involved borane (BH3) It sim phfies our mechanistic analysis and is at variance with reality only m matters of detail Borane is electrophilic it has a vacant 2p orbital and can accept a pair of electrons into that orbital The source of this electron pair is the rr bond of an alkene It is believed as shown m Figure 6 10 for the example of the hydroboration of 1 methylcyclopentene that the first step produces an unstable intermediate called a tt complex In this rr com plex boron and the two carbon atoms of the double bond are joined by a three center two electron bond by which we mean that three atoms share two electrons Three center two electron bonds are frequently encountered m boron chemistry The tt complex is formed by a transfer of electron density from the tt orbital of the alkene to the 2p orbital... 

Motor-driven reciprocating compressors above about 75 kW (100 hp) in size are usually equipped with a step control. This is in reality a variation of constant-speed control in which unloading is accomplished in a series of steps, varying from full load down to no load. Three-step eontrol (full load, one-half load, and no load) is usually accomplished with inlet-valve unloaders. Five-step eontrol (fuU load, three-fourths load, one-half load, one-fourth load, and no load) is accomphshed by means of clearance pockets (see Fig. 10-91). On some machines, inlet-valve and clearance-control unloading are used in combination. 

The stress intensity factor is a means of characterising the elastic stress distribution near the crack tip but in itself has no physical reality. It has units of MN and should not be confused with the elastic stress concentration factor (K,) referred to earlier. 

The basic goal of quality management is the elimination of failure both in the concept and in the reality of our products, services, and processes. In an ideal world, if we could design products, services, and processes that could not fail we would have achieved the ultimate goal. Failure means not only that products, services, and processes would fail to fulfill their function but that their function was not what our customers desired. A gold-plated mousetrap that does not fail is not a success if no one needs a gold-plated mousetrap ... 

The chemical reactions that occnr in flames transform an initial reactant mixtnre into final reaction prodncts. In the case of fnel-oxygen combns-tion, the final prodncts are principally water vapor and carbon dioxide, althongh nnmerons other prodncts snch as carbon monoxide may be formed, depending on the reactant composition and other factors. If the ratio of fnel-to-oxygen is stoichiometric, the final reaction prodncts, by definition, contain no excess fnel or oxygen. Theoretically, this means that partial oxidation prodncts snch as CO (itself a fnel) are not formed. In reality, partial oxidation prodncts snch as CO or OH are formed by high tem-peratnre reactions. For example, the molar stoichiometric reaction of methane is written ... 

At the other end of the spectrum are the ab initio ( from first principles ) methods, such as the calculations already discussed for H2 in Chapter 4. I am not trying to imply that these calculations are correct in any strict sense, although we would hope that the results would bear some relation to reality. An ab initio HF calculation of the potential energy curve for a diatomic Aj will generally give incorrect dissociation products, and so cannot possibly be right in the absolute sense. The phrase ab initio simply means that we have started with a certain Hamiltonian and a set of basis functions, and then done all the intermediate calculations with full rigour and no appeal to experiment. 

The distinction between objects is fundamentally subjective. Objects have no meaning (or reality) in isolation. The identity and characteristics of an object are functions of the total web of inter-relationships that object has with all other objects, on all (emergent) levels of a system. Objects may take on different identities and characteristics that depend on their local context. 

Reality Check This extremely high concentration, 40 M, means that Zn(OH)2 is completely soluble in acid at pH 5 (or any lower pH). 

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