Stoichiometry Coefficient

Fig. 5. Temperature dependence of the stoichiometry coefficient v for the homogeneous decomposition of hydrazine from shock tube data. , ps2h4 = 11.6, pt = 0.7 9, Fn2h4 = 5.0, Px 1-2 , Pn2h4 = 2.2, pt = 2.5 O, Pn2h4 = 1-2, pt = 1.2 Pn2h4 = 11 Pt = 2.5 Q, Pn2h4 = 11, Pt = 5.7, Q, pm2h4 = 7.4 px = 7.5. pn2h4 = partial density of N2H4 in 10 5 mole.l-1 pt — total density at reaction conditions in 10-2 mole.l". (From Michel and Wagner28.)...

As shown by equation 2.11, known as the Kirchhofif equation, the standard reaction heat capacity (ArC°) is the difference between the standard heat capacities of the products and reactants (recall that v are the stoichiometry coefficients—negative for the reactants and positive for the products) ... 

A Remember "grams to moles to moles to grams." Step 1 converts mass to moles for the known value. In this case, kg and kmol are used. Step 2 relates moles of the known value to moles of the unknown value by their stoichiometry coefficients. Step 3 converts moles off the unknown value to a mass. 

When the airflow rate is doubled to 2 L min the low-frequency arc vanishes, as shown in Figure 6.38. This can be explained by a change in the stoichiometry coefficient and a decrease in liquid water content in the GDL as more water is removed from the cell via the air stream. With an air flow rate of only 1 L min 1 there is no significant performance loss. Since the variations between the individual cell voltages do not vanish at higher airflow rates, the variations are not attributable to improper air distribution within the stack. 

Thermochemistry pertains to changes in energy or enthalpy that accompany chemical reactions generally one deals with the heat of reaction which refers to the quantity of heat Q that must be absorbed or released at the end of a process in order that the temperature at the conclusion of the reaction shall be the same as at the outset. As follows from the discussion of Section 1.19, at constant volume Qy — AEd, whereas at constant pressure QP - AHd. Here, AEd - Sd E and AHd - Sd A. wherein, as before, the vt are the stoichiometry coefficients in the chemical reaction S(1) iAi - 0, and < 0 or > 0 according to whether one deals with reagents or products. It is customary to provide all information normalized to 25°C and P - 1 atm. Where experimental data are taken under other conditions the data are corrected for standard conditions as discussed in Section 1.18 see also Exercise 3.8.1. 

The equilibrium constant actually involves a ratio of partial pressures, since the stoichiometry coefficients of the reagents are negative. Eq. (2.9.5b) is in the standard form used to represent equilibrium constants in terms of composition variables. 

In most general terms, one starts with the overall criterion for chemical equilibrium, (Y,i T//x/)eq = 0, developed in Section 2.9. Here again the v/ indicate stoichiometry coefficients for the generalized chemical reaction = 0 where... 

Fokkink et al. [35] argue that for divalent metal cations the proton stoichiometry coefficient as a function of (PZC-pH) should give one bell shaped master curve for all oxides and all metal cations, with a maximum r value slightly below 2 for PZC-pH = 0 and r = 1 at PZC-pH = 4. They support their calculations by experimental data from six sources covering seven adsorbents and six metal cations. 

FIG. 4.13 (A) The difference in the proton charge of alumina induced by the presence of 10 mol dm" of phosphate (total concentration), calculated from the charging curves in Fig. 4.11 (A). (B) The proton stoichiometry coefficient calculated from the curves shown in Fig. 4.13 (A). 

The proton stoichiometry coefficients taken from literature are compared with reciprocal slope of log-log adsorption isotherms at constant pH The agreement wa.s good with Cd and Cu (r = 1 8 and I 9. respectively), but rather poor wtth Zn... 

Components A, B,... are consumed by the reaction and have negative stoichiometry coefficients so that m = —VA,n=—VB,--- are positive (or zero). For elementary reactions, m and n must be integers of 2 or less and, practically speaking, must sum to 2 or less so that the only real possibilities for elementary reactions are first and second order. 

The same reacting mixture may be described by infinite numbers of systems of n-h independent chemical reactions equivalently (each of such systems corresponds to some choice of basis gP in V) which may be mutually recalculated by linear transformations of the type (A.87). Using (4.40), we recalculate the corresponding stoichiometry coefficients zero column for non-reacting constituent a will be again zero. Therefore, reacting and non-reacting constituents are such in any choice of the system of independent chemical reactions. 

In LSE the concentrations of the mobile ions are usually known and fixed by the composition of the LE. This is certainly true for strong electrolytes where the concentration of the mobile ions is equal to the concentration of the corresponding material added to the solution, times the stoichiometry coefficient. 

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