Use the data of Hu et al. (1995) in Fig. 5.19 to derive the second-order rate constant for the O, + I" reaction in the liquid phase assuming that solubility and gas-phase diffusion are not limiting factors. Also derive a value for the mass accommodation coefficient for O-, based on these data. The Henry s law constant for O-, can be taken to be 0.02 M atm-1, the temperature is 277 K, and the diffusion coefficient in the liquid phase 1.3 X 10-5 cm2 s-1. [Pg.175]

Chemical kinetics govern the rate at which chemical species are created or destroyed via reactions. Chapter 9 discussed chemical kinetics of reactions in the gas phase. Reactions were assumed to follow the law of mass action. Rates are determined by the concentrations of the chemical species involved in the reaction and an experimentally determined rate coefficient (or rate constant) k. [Pg.401]

From the measurements of the effective uptake coefficient, the aqueous phase reaction rate constant can be calculated, as long as the gas phase and liquid phase diffusion coefficients and the Henry constant are known. As mentioned, a gas transfer into droplets is characterized by the continuum regime. The unsteady-state diffusion flux (it means that depends on t as well as on x) of species A along the x-axis to the stationary droplet (Fig. 4.20) was described by Seinfeld and Pandis (1998), where c x, t) is the concentration, depending on time and location [Pg.439]

Now it is possible to develop a strategy for analyzing the time dependence of total pressure for gas-phase reactions when the sum of stoichiometric coefficients does not vanish. Since the order of the forward and backward reactions is known for elementary steps, linear least-squares analysis via the differential approach is useful to determine the forward kinetic rate constant if the equilibrium constant can be calculated from thermodynamics. The logical sequence of steps is as follows [Pg.141]

Example 17.1-2 The reaction rate in a large catalyst pellet We want to set up a packed-bed laboratory reactor to study a first-order reaction for which the rate constant is 18.6 sec We plan to use 0.6 cm spheres of a porous catalyst for this gas-phase reaction. The diffusion coefficient of reagents in these particles is about 0.027 cm /sec. [Pg.486]

The rate constants (/c[and k]) and the stoichiometric coefficients (t and 1/ ) are all assumed to be known. Likewise, the reaction rate functions Rt for each reaction step, the equation of state for the density p, the specific enthalpies for the chemical species Hk, as well as the expression for the specific heat of the fluid cp must be provided. In most commercial CFD codes, user interfaces are available to simplify the input of these data. For example, for a combusting system with gas-phase chemistry, chemical databases such as Chemkin-II greatly simplify the process of supplying the detailed chemistry to a CFD code. [Pg.267]

Thermochemical properties of gas-phase, surface, and bulk species are assumed to be available. This information is used in the calculation of the equilibrium constant, Eq. 11.110, and thus the reverse rate constant, Eq. 11.108. There is not a great deal of thermochemical data for species on surfaces, but techniques are becoming available for their calculation (e.g., Pederson et al. [310]). If surface reactions are specified to be irreversible, or if Arrhenius coefficients for the reverse rate constant are explicitly supplied, then the thermochemical data are not actually used. [Pg.469]

The chemist or engineer designing his experiments to establish quantitative kinetics of gas-phase reactions will do his best to look for constant-volume equipment. However, occasionally he may have to work with data obtained at constant pressure. The complication here is that a change in mole number affects the reaction volume and, thereby, the concentrations of the participants, distorting their histories from which reaction orders and rate coefficients are deduced Volume variation disguises kinetics and must be corrected for. [Pg.52]

Equations (1.3-14) and (1.3-15) thus give the prediction from transition-state theory for the rate of a reaction in terms appropriate for an SCF. The rate is seen to depend on (i) the pressure, the temperature and some universal constants (ii) the equilibrium constant for the activated-complex formation in an ideal gas and (iii) a ratio of fugacity coefficients, which express the effect of the supercritical medium. Equation (1.3-15) can therefore be used to calcu-late the rate coefficient, if Kp is known from the gas-phase reaction or calculated from statistical mechanics, and the ratio (0a 0b/0cO estimated from an equation of state. Such calculations are rare an early example is the modeling of the dimerization of pure chlorotrifluoroethene = 105.8 °C) to 1,2-dichlor-ohexafluorocyclobutane (Scheme 1.3-2) and comparison with experimental results at 120 °C, 135 °C and 150 °C and at pressures up to 100 bar [15]. [Pg.60]

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