Stoichiometric calculations defined

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. 

The applications of chemistry focus primarily on chemical reactions, and the commercial use of a reaction requires knowledge of several of its characteristics. A reaction is defined by its reactants and products, whose identities must be learned by experiment. Once the reactants and products are known, the equation for the reaction can be written and balanced and stoichiometric calculations can be carried out. Another very important characteristic of a reaction is its spontaneity. Spontaneity refers to the inherent tendency for the process to occur however, it implies nothing about speed. Spontaneous does not mean fast. There are many spontaneous reactions that are so slow that no apparent reaction occurs over a period of weeks or years at normal temperatures. For example, there is a strong inherent tendency for gaseous hydrogen and oxygen to combine to form water,... 

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 ... 

Briefly define and explain the mole ratio method of stoichiometric calculations. 

Adiabatic Reaction Temperature (T ). The concept of adiabatic or theoretical reaction temperature (T j) plays an important role in the design of chemical reactors, gas furnaces, and other process equipment to handle highly exothermic reactions such as combustion. T is defined as the final temperature attained by the reaction mixture at the completion of a chemical reaction carried out under adiabatic conditions in a closed system at constant pressure. Theoretically, this is the maximum temperature achieved by the products when stoichiometric quantities of reactants are completely converted into products in an adiabatic reactor. In general, T is a function of the initial temperature (T) of the reactants and their relative amounts as well as the presence of any nonreactive (inert) materials. T is also dependent on the extent of completion of the reaction. In actual experiments, it is very unlikely that the theoretical maximum values of T can be realized, but the calculated results do provide an idealized basis for comparison of the thermal effects resulting from exothermic reactions. Lower feed temperatures (T), presence of inerts and excess reactants, and incomplete conversion tend to reduce the value of T. The term theoretical or adiabatic flame temperature (T,, ) is preferred over T in dealing exclusively with the combustion of fuels. 

When plotted on a graph of pH vs. volume of NaOH solution, these six points reveal the gross features of the titration curve. Adding additional calculated points helps define the pH curve. On the curve shown here, the red points A-D were calculated using the buffer equation with base/acid ratios of 1/3 and 3/1. Point E was generated from excess hydroxide ion concentration, 2.00 mL beyond the second stoichiometric point. You should verify these additional five calculations. 

From changes in free energy in standard reference conditions it is possible to calculate equilibrium constants for reactions involving several reactants and products. Consider, for example, the chemical reaction aA + bB = cC + dD at equilibrium in solution. For this reaction we can define a stoichiometric equilibrium constant in terms of the concentrations of the reactants and products as... 

This permits provisional calculation of the compositional dependence of the equilibrium constant and determination of provisional values of the solid phase activity coefficients (discussed below). The equilibrium constant and activity coefficients are termed provisional because it is not possible to determine if stoichiometric saturation has been established without independent knowledge of the compositional dependence of the equilibrium constant, such as would be provided from independent thermodynamic measurements. Using the provisional activity coefficient data we may compare the observed solid solution-aqueous solution compositions with those calculated at equilibrium. Agreement between the calculated and observed values confirms, within the experimental data uncertainties, the establishment of equilibrium. The true solid solution thermodynamic properties are then defined to be equal to the provisional values. 

The matrices defining the Model and the p-values are contained in the upper part of the spreadsheet. The given total concentrations of M and L are collected in the columns A and B, row 8 downwards. Initially guessed values for the component concentrations [M and [L] for each solution are in the respective rows of columns D and E. The next two entries, [ML] and [ML2], are calculated from the component concentrations and the respective formation constant, according to equation (3.23). Next, the calculated total concentrations are computed, making sure the stoichiometric coefficients are incorporated correctly, equation (3.30). The task is to juggle the initially estimated component concentrations [M and [L] in columns D and E until the calculated total concentrations collected in the columns I and J match the known concentrations in the columns A and B. The reader is encouraged... 

Thermodynamic modelling of solution phases lies at the core of the CALPHAD method. Only rarely do calculations involve purely stoichiometric compounds. The calculation of a complex system which may have literally 100 different stoichiometric substances usually has a phase such as the gas which is a mixture of many components, and in a complex metallic system with 10 or 11 alloying elements it is not unusual for all of the phases to involve solubility of the various elements. Solution phases will be defined here as any phase in which there is solubility of more than one component and within this chapter are broken down to four types (1) random substitutional, (2) sublattice, (3) ionic and (4) aqueous. Others types of solution phase, such as exist in polymers or complex organic systems, can also be modelled, but these four represent the major types which are currently available in CALPHAD software programmes. 

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. 

In Eq. (10) z is the stoichiometric coefficient of the ozone-compound reaction [reaction (8)], Z)M is the diffusivity of compound M in water (which can be calculated from the Wilke and Chang equation), and C o3 is the ozone solubility (or properly defined, the ozone concentration at the gas-water interface). If the parameters of Eqs. (9) and (10) are known, the kinetic regime can be established, and hence the kinetics of ozonation can be determined. Table 3 gives the kinetic equations corresponding to different kinetic regimes found in ozonation processes. As can be deduced from the equations in Table 3, the rate constant, mass transfer coefficients, and ozone solubility must be previously known to establish the actual ozonation kinetics. The literature reports extensive information on research studies dealing with kinetic parameter determination as quoted below. 

Two useful measures of the potential environmental acceptability of chemical processes are the E factor [12-18], defined as the mass ratio of waste to desired product and the atom efficiency, calculated by dividing the molecular weight of the desired product by the sum of the molecular weights of all substances produced in the stoichiometric equation. The sheer magnitude of the waste problem in chemicals manufacture is readily apparent from a consideration of typical E factors in various segments of the chemical industry (Table 1.1). 

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. 

In this equation A, is the iih reactant or product and V is the stoichiometric coefficient of this species (negative for reactants and positive for products). It is also convenient to define u, for each inert species in the feed to the reactor, assigning it a value of 0. The inputs to the module are the feed stream flow rate, composition, and temperature, the fractional conversion of one of the reactants, and the product stream temperature. The module is to calculate the product stream component flow rates and the required heat transfer to the reactor. 

In defining conversion, we choose one of the reactants as the basis of calculation and then relate the other species involved in the reaction, to this basis. In most instances it is best to choose the limiting reactant as the basis of calculation. We develop the stoichiometric relationships and design equations by considering the general reaction... 

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