Fundamentals of Stoichiometry

Stoichiometry is a term used to describe quantitative relationships in chemistry. Any chemistry question that asks How much of a particular substance will be consumed or formed in a given chemical reaction is a stoichiometry problem. At the heart of every such stoichiometry problem, you ll always find a balanced chemical equation. 

We have seen already that chemical equations are always written in terms of the numbers of particles involved. Whether we interpret them in terms of individual molecules or moles of molecules, the stoichiometric coefficients that balance a chemical equation refer to numbers of particles and not to masses. Usually, we can t measure the number of particles directly in the laboratory masses and volume of liquids are the quantities that are more likely to be measurable. Thus if we want to make quantitative calculations for a chemical reaction, fi-equently we need to convert between the measured value of a mass or volume and the desired value of a number of moles. Because such calculations are common and important, chemists have developed a standard approach to overcome this variable mismatch. Although you might think of this approach as an algorithm for solving a particular class of chemistry problems, it is instructive to understand its conceptual 

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In most industrially relevant reacting systems, one main reaction typically makes the desired products and several side reactions make byproducts. The specific rate of production or consumption of a particular component in such a reaction set depends upon the stoichiometry and the rates. For example, assume that the main reaction for making vinyl acetate, Eq. (4.4.1, proceeds with a rate r< (mol/L s) and that the side reaction, Eq. (4.8), proceeds with rate r2 (mol/L s). Then the net consumption of ethylene is (-l)r1 - (-1 )r2 (mol/L s). Similarly, the net consumption of oxygen is (-0.5)fi + (— 3)r2, and the net production of water is (l)r-, + (2)ra. For a given chemistry (stoichiometry), our ability to control the production or consumption of any one component in the reactor is thus limited to how well we can influence the various rates. This boils down to manipulating the reactor temperature and/ or the concentrations of the dominant components. Occasionally, the reaction volume for liquid-phase reactions or the pressure for gas-phase reactions can also be manipulated for overall production control. These are the fundamentals of reactor control. 

Goldberg Fundamentals of I 10. Stoichiometry Chemistry, Fifth Edition... 

Implied in the stoichiometry of their preparation is the full equivalent of transition metal relative to substrate. Indeed, to this day, cuprates tend to be used in excess in most smaller scale reactions. Over the past decade, however, there has been a noticeable shift toward development of methodology catalytic in Cu(I). The rationale behind the emphasis is in line with the times that is, environmental concerns have come to the fore, placing implied limits on the extent of transition metal usage. Therefore, notwithstanding favorable economic factors associated with copper, it being a base rather than precious metal, much effort has been devoted toward copper-catalyzed reactions, including cross-couplings to arrive at C-N, C-O, and C-H, in addition to C-C bonds. Moreover, tremendous strides have been made in asymmetric versions of perhaps the most fundamental of cuprate reactions 1,4-additions to Michael acceptors. 

Our objective in this chapter is to begin the subject of stoichiometry, the quantitative study of chemical reactions. This will help us determine, for example, what quantity of oxygen is required for complete combustion of a given quantity of glucose or what mass of carbon dioxide can be obtained. Stoichiometry is a part of chemistry that is fundamental to much of what chemists, chemical engineers, biochemists, molecular biologists, geochemists, and many others do. 

In addition, there are laws that are fundamentally and necessarily chemical. The laws of stoichiometry and of valency, and the so-called Periodic Law on which Mendeleev based his classification, are examples of laws that are clearly a part of the corpus of chemistry as such. 

There are a number of different fundamental invariants associated with our three-stage description. They relate not only to classical questions of stoichiometry, but also to questions of strain as mediated by some basic differential-geometric theorems involving curvatures. 

Lucretius poem suggests that the Law of Conservation of Matter has been assumed for at least two millennia. It was certainly a fundamental scientific assumption during the scientific revolution. However, it was Lavoisier who propounded the view that, unless all material mass could be accounted for in a chemical reaction, one could not even try to understand it. Critical, too, were Richter s establishment of tables of equivalents and his concept of stoichiometry and Proust s law of definite composition, that successfully survived his debate with Berthollet. Dalton s notebook entry on September 6, 1803 (his thirty-seventh birthday) includes the first symbolic drawings and relative weights of his atoms. ... 

From the foregoing it is clear that the theory of elemental balance is an invaluable tool in the description of the systems commonly encountered in bioengineering. It is as fundamental as stoichiometry in chemical reaction engineering systems. The theory seems to be well developed, and the field is open to the development of specific applications. A significant problem is, however, associated with the application of the theory. It applies to instances in which more flows are measured than are minimally needed to calculate the remaining ones. In this case, a statistical procedure can be applied to obtain a more optimal estimate of all measured and unknown flows. 

Although the apatite crystals undoubtedly are fundamental to bone structure, a number of problems remain unsolved. Among them are the lack of stoichiometry in the composition of the mineral phase of bone, and the exact morphological appearance of the crystal. 

The reaction-rate constant vanishes as the TPP to PN ratio approaches zero, whereas an uncatalyzed reaction would be evidenced by a nonzero reaction rate constant when Cto/Cpo equals zero. The intersection at the origin implies that no significant uncatalyzed reaction occurs. The linearity of the plot indicates that the only catalytic mechanisms which occur are those which are fundamentally dependent on the same types of interactions between TPP and the other reactants in the range of stoichiometries examined (R = 0.50 to 1.30). 

This chapter mainly deals with the fundamentals of H2/air PEM fuel cells, including fuel cell reaction thermodynamics and kinetics, as well as a brief introduction to the single fuel cell and the fuel cell stack. The electrochemistry and reaction mechanisms of H2/air fuel cell reactions, including the anode HOR and the cathode ORR, are discussed in depth. Several concepts related to PEM fuel cell performance, such as fuel cell polarization curves, OCV, hydrogen crossover, and fuel cell efficiencies, are also introduced. With respect to fuel cell stmctures and components, the material properties and effects on fuel cell performance are also discussed. In addition, several important conditions for fuel cell operation, including temperature, pressure, RH, and gas stoichiometries and flow rates, and their effects on fuel cell operation, are also briefly presented. This chapter provides the requisite baseline knowledge for the remaining chapters. 

The observed emf dtrring the titration provides fundamental information on the thermodynamics of the system in addition to the phase eqtrilibria. The knowledge of the emf as a function of stoichiometry allows the determination of thermodynamic data with high resolution as a function of the composition of the sample. 

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