SECTION 5 Classifying Chemical Reactions

You can get the same kind of information from a balanced chemical equation. In Chapter 4, you learned how to classify chemical reactions and balance the chemical equations that describe them. In Chapters 5 and 6, you learned how chemists relate the number of particles in a substance to the amount of the substance in moles and grams. In this section, you will use your knowledge to interpret the information in a chemical equation, in terms of particles, moles, and mass. Try the following Express Lab to explore the molar relationships between products and reactants. 

In Chapter 7, we learned how to do nnmerical calculations for compounds, using their formulas as a basis. This chapter lays the foundation for doing similar calculations for chemical reactions, using the balanced equation as a basis. The chemical equation is introduced in Section 8.1, and methods for balancing equations are presented in Section 8.2. To write equations, we must often be able to predict the products of a reaction from a knowledge of the properties of the reactants. Section 8.3 shows how to classify chemical reactions into types to predict the products of thousands of reactions. An important type of reaction— the acid-base reaction— is discussed in Section 8.4. 

There is another common way to classify chemical reactions acid-base reactions, oxidation-reduction reactions, and reactions of more complicated types (beyond the scope of this book). Acid-base reactions are considered to involve the reactions of hydrogen ions with hydroxide ions. The reactions of acids and bases will be taken up in this section, and a more sophisticated view of these reactions is presented in Chapter 19. Oxidation-reduction reactions involve the transfer of electrons from one substance to another. Many combination reactions, many decomposition reactions, all single substitution reactions, and all combustion reactions are of this type, but more complex examples are presented in Chapters 16 and 17. 

What are two different ways to classify chemical reactions presented in Section 7.10 Explain the differences between them. 

In Section 3.9, we classify chemical reactions according to whether they absorb or emit heat energy in tiie course of the reaction. Recall that an exothermic reaction (one witii a negative emits heat. 

There are several ways to classify chemical reactions, and none are entirely satisfactory. The classification scheme described in this section provides an introduction to five basic types of reactions synthesis, decomposition, singledisplacement, double-displacement, and combustion reactions. In later chapters, you will be introduced to categories that are useful in classifying other types of chemical reactions,... 

In the last section we examined some of the categories into which polymers can be classified. Various aspects of molecular structure were used as the basis for classification in that section. Next we shall consider the chemical reactions that produce the molecules as a basis for classification. The objective of this discussion is simply to provide some orientation and to introduce some typical polymers. For this purpose a number of polymers may be classified as either addition or condensation polymers. Each of these classes of polymers are discussed in detail in Part II of this book, specifically Chaps. 5 and 6 for condensation and addition, respectively. Even though these categories are based on the reactions which produce the polymers, it should not be inferred that only two types of polymerization reactions exist. We have to start somewhere, and these two important categories are the usual place to begin. 

The overall stability of the complexes listed in Table II tends to parallel, but exceed, that of their alkyl counterparts. Their chemical reactions may be classified as shown in the headings to Sections II,C,l-5, respectively, of which the Si—M cleavages (Section II,C,3) have been the most studied. 

After understanding the generation of various free radicals as a result of ultrasonic propagation and cavitation in pure water as well as in the presence of different gases, we can perhaps understand the aqueous chemical reactions better. However, for the sake of simplicity, all reactions involving inorganic species, have been broadly classified into following sections and would be taken up one by one... 

From among the different classes of compounds considered in this work, most of the computational work was done on amines, while less examples are found for nitro compounds and very few for nitroso ones. The different studies may be classified into several major areas (1) conformational analysis and structural investigation (2) spectroscopic experiments and study of chemical effects (3) investigation of chemical reactions mechanism (4) heats of formation and density calculations, especially of high energetic materials. In the following sections we will concentrate on molecular mechanics based research studies, or on such where molecular mechanics calculations played a... 

As mentioned in Chapter 1, Section 2.2, it is quite common that a heterogeneous electron transfer process is complicated by homogeneous chemical reactions that involve the species Ox and/or Red. In this light, the chemical complications are classified as ... 

In this section, you learned how to relate the rate of a chemical reaction to the concentrations of the reactants using the rate law. You classified reactions based on their reaction order. You determined the rate law equation from empirical data. Then you learned about the half-life of a first-order reaction. As you worked through sections 6.1 and 6.2, you may have wondered why factors such as concentration and temperature affect the rates of chemical reactions. In the following section, you will learn about some theories that have been developed to explain the effects of these factors. 

Chemical reactions may be classified by the number of phases involved in the reaction. If the reaction takes place inside one single phase, it is said to be a homogeneous reaction. Otherwise, it is a heterogeneous reaction. For homogeneous reactions, there are no surface effects and mass transfer usually does not play a role. Heterogeneous reactions, on the other hand, often involve surface effects, formation of new phases (nucleation), and mass transfer diffusion and convection). Hence, the theories for the kinetics of homogeneous and heterogeneous reactions are different and are treated in different sections. 

Chemical reactions are classified usually as diffusion-controlled, whose rate is limited by a reactant spatial approach to each other, and reaction-controlled (kinetic stage), whose rate is limited by a reaction elementary event. For systems with ideal reactant mixing considered in Section 2.1.1, there is no mechanism of reactant mutual approach. On the other hand, the kinetic equations (2.1.40) distinguish between reaction in physically infinitesimal volumes and the distant reactant motion in a whole reaction volume. In the absence of reaction particle diffusion is described by equation... 

The methods that have been utilized to prepare the cationic metal carbonyls cover an exceedingly wide range of chemical reactions. An effort has been made to classify these in Sections A to H below. 

Stability constants are not always the best predictive tool for measuring the ease and the extent of chemical reactions involving complexes nor their stability with time, because their kinetic behavior can often be even more crucial. For example, when ligand exchange reactions of ML (e.g., [FeEDTA]) with other metal ions (e.g., Zn2+ or Ca2+) are ki-netically slow, they do not significantly influence ligand speciation. Another typical example of the thermodynamics vs kinetics competition is the fact that the degradability of some metal complexes (e.g., metal-NTA) is related to their kinetic lability, rather than to their thermodynamic stability constants. Kinetic rather than thermodynamic data are then used to classify metal complexes as labile, quasi-labile, slowly labile, and inert (or stable). See Section 3.2.6. 

There are roughly ten million classified chemical compounds at the present time. Each individual molecule has many properties to compute and/or measure binding energy, electron density, atomic structure, spectra (vibrational, rotational and electronic), reaction rates, electron and molecular scattering cross sections. However, the spectacular opportunity for the future lies in compounds not yet synthesized or classified. The number of unexplored forms of matter which can fit into a small box one centimeter on a side is... 

To coincide with the organization of the first part [99AHC(73)131], this chapter is also classified into five major sections Introduction, Synthesis, Reactions, Spectral properties, and Applications. The literature has been searched to issue number 10 volume 129,1998 of Chemical Abstracts. 

Many chemical reactions involve a catalyst. A very general definition of a catalyst is a substance that makes a reaction path available with a lower energy of activation. Strictly speaking, a catalyst is not consumed by the reaction, but organic chemists frequently speak of acid-catalyzed or base-catalyzed mechanisms that do lead to overall consumption of the acid or base. Better phrases under these circumstances would be acid promoted or base promoted. Catalysts can also be described as electrophilic or nucleophilic, depending on the catalyst s electronic nature. Catalysis by Lewis acids and Lewis bases can be classified as electrophilic and nucleophilic, respectively. In free-radical reactions, the initiator often plays a key role. An initiator is a substance that can easily generate radical intermediates. Radical reactions often occur by chain mechanisms, and the role of the initiator is to provide the free radicals that start the chain reaction. In this section we discuss some fundamental examples of catalysis with emphasis on proton transfer (Brpnsted acid/base) and Lewis acid catalysis. 

The chemical reactions described in this Section are classified, as far as possible, according to the functions of the 1,2,4-thiadiazole structure, but some overlap has occurred when related results are summarized more effectively and briefly in one place. For the same reason some reactions have already been dealt with in the context of the syntheses. 

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