Limiting reactant defined

To simplify calculations, but also by convention, the amount of excess reactant in a reaction is defined on the basis of the reaction going to completion for the limiting reactant. In the case of methane (CH4) burned with excess air, the volume of air needed to combust the methane is calculated as though there is complete combustion of the methane, converting it entirely to carbon dioxide and water. 

Selectivity is defined as the ratio of the desired product to the amount of limiting reactant tliat has undergone chemical change. That is... 

In the present study, we carried out the hydrogenation of CO2. We did not use any inert components in the feed. We changed the value of r by changing the molar ratio of H2 to CO2 in the feed gases, a. The parameter p is defined as the volume ratio of the product gas to the reactant gas when the reaction completely proceeds under a constant pressure. The extent of the gas-volume reduction is affected by the stoichiometric relation of the reaction and the content of the inert components in the feed. As given in Eq.(l), p is the function of only the parameter a and the expression of p is affected by a. When a > 4, the limiting reactant is H2, while it is CO2 in the case of a < 4. 

C04-0045. Define each of these terms (a) percent yield (b) limiting reactant (c) spectator ion (d) precipitate (e) titration and (f) oxidation. 

The variable / depends on the particular species chosen as a reference substance. In general, the initial mole numbers of the reactants do not constitute simple stoichiometric ratios, and the number of moles of product that may be formed is limited by the amount of one of the reactants present in the system. If the extent of reaction is not limited by thermodynamic equilibrium constraints, this limiting reagent is the one that determines the maximum possible value of the extent of reaction ( max). We should refer our fractional conversions to this stoichiometrically limiting reactant if / is to lie between zero and unity. Consequently, the treatment used in subsequent chapters will define fractional conversions in terms of the limiting reactant. 

Equation 2.2-2 may appear in various forms, if nA is related to other quantities (by normalization), as follows (1) If A is the limiting reactant, it may be convenient to normalize nA in terms of /A, the fractional conversion of A, defined by ... 

To make 0 limiting reactant so that this reactant disappears and X approaches unity when the reaction is complete. We can then define aU species through the relation... 

The limiting reactant is what will ran out fust during the reaction, i.e. the reactant whose quantity is less than that defined by the stoichiometry of the reaction. Note that the fluid volume (VL) is generally a variable, i.e. a function of time. If the volume of the reaction mixture is constant, eq.(3.71) becomes... 

Suppose that A is in great excess in the gas phase and that its solubility is much lower than that of B. Under this condition, although A is in excess in the gas phase, it could control the reaction rate in the liquid phase where the reaction takes place. However, considering the whole reaction system, i.e. the gas and liquid phase, B will run out first and is the real limiting reactant, as defined earlier. Now consider the reaction rate... 

Predictable Peak Exposures. Ceiling limits, as defined, should be applied only to situations where the periods of maximum exposure can be prospectively identified. If the highest exposure can be anticipated, then its measurement is a physical problem, not a statistical one. All pertinent information related to the operation should be considered so that only air samples which are likely to represent peak air concentrations are collected. Consider, for instance, exposures of workers in a chemical plant to hydrogen sulfide (a reactant in a process). If analysis of the operation shows that the highest exposure should occur when a valve is opened to vent the reaction vessel, then only this period needs to be sampled to determine the peak exposure. 

Two concepts are often used to describe the behaviour of a process involving reactions conversion and selectivity. Conversion is defined with respect to a particular reactant, and it describes the extent of the reaction that takes place relative to the amount that could take place. If we consider the limiting reactant, the reactant that would be consumed first, based on the stoichiometry of the reaction, the definition of conversion is straight forward ... 

The input data defining column configurations, feed, feed composition, column holdup, etc. are given in Table 11.10. The reaction is modelled by simple rate equations (Table 11.10). The batch time is 12 hrs (ts). The objective of the study was to maximise the conversion (X) of the limiting reactant and to obtain the main product with purity of 0.7 molefraction by optimising the reboil ratio defined as V/L. The following optimisation problem (PI) was considered. Model type III was considered with chemical reaction. 

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... 

Define excess reactant, limiting reactant, conversion, degree of completion, and yield in a reaction. 

If one starts out with 1 mol of methane and 3 mol of oxygen in a reaction vessel, only 2 mol of oxygen would be used up, leaving an excess of 1 mol. In this case, the oxygen is called the excess reactant and methane is the limiting reactant. The limiting reactant is defined as the reactant that would be completely consumed if the... 

For gas-phase flow reactors, conversion of the key-limiting reactant (i.e., CO) is typically defined in terms of its molar flow rate (i.e.. Fa) ... 

The conversion, x, is defined as the fraction (or percentage) of the more important or limiting reactant that is consumed. With two reactants A and B and a nearly stoichiometric feed, conversions based on each reactant could be calculated and designated and xg. In most cases, this is not necessary, and only one conversion is calculated based on A, the limiting reactant, and no subscript is needed for x. 

The conversion is the most used variable. It is defined by the number of moles transformed or formed at a given time or local in relation to the initial number of moles. The conversion should always be defined for the limiting reactant of the reaction. The conversion has no unit, ranging from 0 to 1 for irreversible reactions or from 0 to Xac for reversible reactions. So, for irreversible reactions in which A is the limiting component, we have ... 

In this case, it is important to note that the conversion is defined in relation to the limiting reactant A. 

Let us consider two CSTR and PFR reactors in series as shown in Figure 17.2e and f or in Figure 17.3a. If initial concentration of A is Cao and volumetric flow is rro, then the initial molar flow is given by Fao- At the exit of the first reactor, we have the concentration Cai and subsequently decreasing concentrations, Ca, i and Ca, 2, until reaching the final concentration. In a system with constant or variable volume, one calculates the corresponding molar flows Fa,. Conversion is defined with respect to the limiting reactant at the inlet of the first reactor such that the conversion varies between 0 and Xa, at the outlet of the last reactor. One should always take as reference the initial... 

Conversion It indicates the progress of the reaction and is defined as the ratio of the amount of the limiting reactant transformed and the total amount fed to the reactor. For the following parallel reactions... 

In chemical reactions with several reactants, the limiting reactant component is defined as that compound which is present in an amount less than the amount necessary for it to react stoichiometrically with the other reactants. Then the percent completion of a reaction is the amount of this limiting reactant actually converted, divided by the amount originally present, times 100. 

---