Stoichiometric calculations definition

Sometimes, the calculation involves a monoprotic acid and a dihydroxy base or another set of conditions in which the relationship is not 1 1. We have to keep track of the various concentrations so that the molarities do not get mixed up. However, stoichiometric calculations involving solutions of specified normalities are even simpler. By the definition of equivalent mass in Chapter 12, two solutions will react exactly with each other if... 

Molality and molarity are each very useful concentration units, but it is very unfortunate that they sound so similar, are abbreviated so similarly, and have such a subtle but crucial difference in their definitions. Because solutions in the laboratory are usually measured by volume, molarity is very convenient to employ for stoichiometric calculations. However, since molarity is defined as moles of solute per liter of solution, molarity depends on the temperature of the solution. Most things expand when heated, so molar concentration will decrease as the temperature increases. Molality, on the other hand, finds application in physical chemistry, where it is often necessary to consider the quantities of solute and solvent separately, rather than as a mixture. Also, mass does not depend on temperature, so molality is not temperature dependent. However, molality is much less convenient in analysis, because quantities of a solution measured out by volume or mass in the laboratory include both the solute and the solvent. If you need a certain amount of solute, you measure the amount of solution directly, not the amount of solvent. So, when doing stoichiometry, molality requires an additional calculation to take this into account. 

In a chemical reaction, there is a definite ratio between the number of moles of a particular reactant or product and the number of moles of any other reactant or product. These ratios are readily seen by simply examining the coefficients in front of the reaction species in the chemical equation. Normally, a stoichiometric calculation is performed to relate the quantities of only two of the reaction participants. The objective may be to determine how much of one reactant will react with a given quantity of another reactant Or, a particular quantity of a product may be desired, so that it is necessary to calculate the quantity of a specific reactant needed to give the amount of product To perform stoichiometric calculations involving only two reaction participants, it is necessary only to know the relative number of moles of each and their molar masses. The most straightforward type of stoichiometric calculation is the mole ratio metiiod defined as follows ... 

The respiratory quotient (RQ) is often used to estimate metabolic stoichiometry. Using quasi-steady-state and by definition of RQ, develop a system of two linear equations with two unknowns by solving a matrix under the following conditions the coefficient of the matrix with yeast growth (y = 4.14), ammonia (yN = 0) and glucose (ys = 4.0), where the evolution of C02 and biosynthesis are very small (o- = 0.095). Calculate the stoichiometric coefficient for RQ =1.0 for the above biological processes ... 

As equation 2.4.8 indicates, the equilibrium constant for a reaction is determined by the temperature and the standard Gibbs free energy change (AG°) for the process. The latter quantity in turn depends on temperature, the definitions of the standard states of the various components, and the stoichiometric coefficients of these species. Consequently, in assigning a numerical value to an equilibrium constant, one must be careful to specify the three parameters mentioned above in order to give meaning to this value. Once one has thus specified the point of reference, this value may be used to calculate the equilibrium composition of the mixture in the manner described in Sections 2.6 to 2.9. 

Note that reactions 2.14, 2.15, and 2.23 involve fractional stoichiometric coefficients on the left-hand sides. This is because we wanted to define conventional enthalpies of formation (etc.) of one mole of each of the respective products. However, if we are not concerned about the conventional thermodynamic quantities of formation, we can get rid of fractional coefficients by multiplying throughout by the appropriate factor. For example, reaction 2.14 could be doubled, whereupon AG° becomes 2AG, AH° = 2AH , and AS° = 2ASf, and the right-hand sides of Eqs. 2.21 and 2.22 must be squared so that the new equilibrium constant K = K2 = 1.23 x 1083 bar-3. Thus, whenever we give a numerical value for an equilibrium constant or an associated thermodynamic quantity, we must make clear how we chose to define the equilibrium. The concentrations we calculate from an equilibrium constant will, of course, be the same, no matter how it was defined. Sometimes, as in Eq. 2.22, the units given for K will imply the definition, but in certain cases such as reaction 2.23 K is dimensionless. 

Because RME accounts for the mass of all reactants, that is, the actual stoichiometric quantities used, and therefore includes yield and atom economy, this combined metric is probably one of the most helpful metrics for chemists to focus attention on how far from green their current processes actually is. However, like many green chemistry metrics, it does take a little bit of thought to calculate in practice, as one has to work to strict definitions of what to include and what to exclude [46] ... 

The distinction between the isoelectric and isoionic states of a protein was first made in a classic paper by S0rensen et at. (1926). Three definitions of the isoionic point were proposed, one of these being the stoichiometrically defined point which we have called the point of zero net proton charge. The other tw o were operational definitions (summarized by Linderstr0m-Lang and Nielsen, 1959). The term isoionic point, as used here, corresponds to one of these two operational definitions, chosen because it always permits calculation of the point of zero net proton charge, which is the only parameter of real interest in the analysis of titration curves. The same choice has been made by Scatchard and Black (1949). 

This is a quahtative statement within a comparison therefore some rules have to be defined whether any possibly catalytic reaction fulfils this criterion or com-plexation of educt(s) or/and product(s) do(es) simply interfere with the stoichiometric reaction or some step thereof, also influencing the turnover kinetics. This means analyzing - measuring, calculating, predicting - the interaction of some metal ion within a metallo-protein on one hand and substrates, products on the other. Ostwald s definition of a catalyst implies the metal ion and with it its coordinative environment not be changed permanently by this transformation which in turn requires the metal binding properties of the substrate and product to differ from each other. 

Stoichiometry is an accounting system used to keep track of what species are formed (or consumed) and to calculate the composition of chemical reactors. Chapter 2 covers in detail the stoichiometric concepts and definitions used in reactor analysis. 

In a balanced equation, the number of moles of one substance is stoichiometrically equivalent to the number of moles of any other substance. The term stoichiometrically equivalent means that a definite amount of one substance is formed from, produces, or reacts with a definite amount of the other. These quantitative relationships are expressed as stoichiometrically equivalent molar ratios that we use as conversion factors to calculate these amounts. Table 3.3 presents the quantitative information contained in the equation for the combustion of propane, a hydrocarbon fuel used in cooking and water heating ... 

We can make similar definitions and calculations concerning acidity measurements. For a water in which acidity is contributed solely by and carbonate species, the endpoint of the total acidity titration is at a pH where a stoichiometric amount of OH has been added to complete the following three reactions ... 

Sedimentary phosphate rocks that are obtained from. insular and cave deposits often contain carbonate apatites that have a lower F content than that of stoichiometric fluorapatite and, according to calculations, contain significant amounts of hydroxyl in their structures. Although some of these carbonate apatites may meet the francolite definition, they have crystallographic, chemical, and other physical properties that differ substantially from those of francolites that contain excess fluorine [7]. These carbonate apatites form a series with end members that contain almost no fluorine (carbonate-hydroxylapatite) (Table 5.4) and end members that are very close in composition to pure fluorapatite and francolites that have almost no carbonate substitution. Members of this series are referred to as hydroxyl-fluor-carbonate apatites in this section. Table 5.5 shows the a-values of some phosphate rocks containing hydroxyl-fluor-carbonate apatites in this series. 

Both the net rate of production and the reaction rate are used in many further data processing procedures, such as the determination of rate coefficients k, pre-exponential factors ko, activation energies kinetic orders, and so on. The definitions of these rates have to be carefully distinguished. The net rate of production of a component is an experimentally observed characteristic. It is the change of the number of moles of a component per unit volume of reactor (or catalyst surface, volume, or mass) per unit time. The reaction rate r can be introduced only after a reaetion equation has been assumed with the corresponding stoichiometric coefficients. Then, the value of the reaction rate can be calculated based on the assumed stoichiometrie reaction equation. This is an important conceptual difference between the experimentally observed net rate of production and the calculated reaction rate, whieh is a result of our interpretation. The main methodologieal lesson is Do not mix experimental measurements and their interpretation. 

We remember from Chapter 5 that the coefficients in equations such as Equation 7.3 allow the relative number of moles of pure reactants and products involved in the reaction to be determined. These relationships coupled with the mole definition in terms of masses then yield factors that can be used to solve stoichiometric problems involving the reactants and products. Similar calculations can be done for reactions that take place between the solutes of solutions if the amount of solute contained in a specific quantity of the reacting solutions is known. Such relationships are known as solution concentrations. Solution concentrations may be expressed in a variety of units, but only two, molarity and percentage, will be discussed at this time. 

The LMO (001) surface was modeled in [852] by similar symmetric 7-plane slabs with two kinds of terminations (LaO LaO and Mn02 Mn02) and an 8-plane LaO Mn02 slab. The former is nonstoichiometric, the latter is stoichiometric (four bulk unit cells per surface unit cell). Unhke the (110) O-terminated surface, it is not easy to make the 7-plane (001) slab stoichiometric through introduction of surface vacancies. If we count the formal ionic charges, La +, Mn ", 0 , these two slabs have the total charges of 1 e (LaO) and -1 e (Mn02) In the SCF calculations, slabs are assumed to be neutral by definition, which results in the electronic-density redistribution between atoms in different planes. 

Note that we have to use the stoichiometric coefficients from the balanced reaction along with the molar H values. It turns out that many of the heats of combustion and use of the definition of the heats of formation of elements as zero lead to a whole series of heats of formation of compounds, which have also been tabulated (see Table 4.2) at length in places like the CRC Handbook [8] for thousands of compounds. This is possible due to the algebraic summation of enthalpy values. Notice that at this point all reactions are considered to be at 25°C. To summarize, heats of combustion can be used to calculate heats of reactions which lead to standard heats of formation at 25°C. 

There are enough data in the preceding table to calculate for each species. If the pilot-plant data are consistent with the hypothesis that one stoichiometrically simple reaction (Reaction (1-B)) took place, then by the Law of Definite Proportions (Eqn. (1-5)), the value of should be the same for all four species. 

If the reactor is closed or partially closed with respect to one or more components, the stoichiometrically least abundant component will be chosen. We can again apply definition [1.14] and equation [1.15] in order to calculate the quantities of different species lost or produced when the system is closed to the fractional extent a. 

Equation (21) is not strictly valid for calculating the heat of micellization because certain assumptions made in its derivation do not hold here. The equation implies that the micelle is at equilibrium near cmc in a standard state [27,54]. However, micelles are not definite stoichiometric entities but aggregates of different sizes that are in dynamic equilibrium with themselves and surfactant monomers. The aggregation number may vary with temperature. An extended mass action model describes micellization as a multiple equilibrium characterized by a series of equilibrium constants (see Section 6.2). Because these equilibrium constants cannot be determined, the micellar equilibrium is usually described by... 

The prime ( ) on the symbol for the mass of the desired product serves to remind us that this mass is calculated for a stoichiometric mixture of reactants. Use the definition above to calculate the percent AE for the following reactions, both of which can be used to make CgHgNH2, the desired product. 

Assuming that the combustion reaction of vacuum residue (dry basis) with stoichiometric supply of oxygen is complete (Equation 4.62), by Hess s law it is possible to calculate the standard enthalpy of formation (H gy) in kJ/kmol (Equation 4.63) (De Souza-Santos, 2004). The enthalpy of combustion of vacuum residue corresponds to low heating value LHV," whose definition is the heat released when a fuel is burned using stoichiometric supply of oxygen ... 

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