Equilibrium in gas phase

When A is not in adsorbtive equilibrium but it is in chemical equilibrium in the gas phase according to 

Reaction Special condition Basic rate equation Driving force Adsorption term 

When an inert substance I is adsorbed, the term is to be added to the adsorption term. 

TABLE 7-5 Adsorption-Rate Controlling (Rapid Surface Reaction) 

SOURCE From Walas, Reaction Kinetics for Chemical Engineers. McGraw-Hill, 1959 Butterworths, 1989. 

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In this part of your study of general chemistry, it is typical to explore how a chemical system comes to equilibrium and how that equilibrium is represented. Interpretation of equilibrium constants, calculation of concentrations in equilibrium systems, equilibrium in gas phase reactions, relationship of enthalpy to equilibrium, acid-base equilibria, and solubility equilibria all fall into this area of study. 

The oxidation of metals by water vapor is carried out in experiments fixing the partial pressures of water and hydrogen (produced gas). The simultaneous presence of these two gases involves, by the action of the chemical equilibrium in gas phase, a partial pressure of oxygen. 

An important example for the application of general first-order kinetics in gas-phase reactions is the master equation treatment of the fall-off range of themial unimolecular reactions to describe non-equilibrium effects in the weak collision limit when activation and deactivation cross sections (equation (A3.4.125)) are to be retained in detail [ ]. 

Perturbation or relaxation techniques are applied to chemical reaction systems with a well-defined equilibrium. An instantaneous change of one or several state fiinctions causes the system to relax into its new equilibrium [29]. In gas-phase kmetics, the perturbations typically exploit the temperature (r-jump) and pressure (P-jump) dependence of chemical equilibria [6]. The relaxation kinetics are monitored by spectroscopic methods. 

A general limitation of the relaxation teclmiques with small perturbations from equilibrium discussed in the previous section arises from the restriction to systems starting at or near equilibrium under the conditions used. This limitation is overcome by teclmiques with large perturbations. The most important representative of this class of relaxation techniques in gas-phase kinetics is the shock-tube method, which achieves J-jumps of some 1000 K (accompanied by corresponding P-jumps) [30, and 53]. Shock hibes are particularly... 

Cjo CO concentration in gas phase equilibrium with liquid phase, mmol COl-1... 

Equilibrium in multiphase and/or multireaction systems. If more than one phase is present in the system, a criterion of phase equilibria has to be satisfied together with the chemical equilibrium criterion. For instance, in a gas-liquid system components are in chemical equilibrium in the phase where the reaction occurs, but vapour-liquid equilibria between the gas and the liquid phases must also be taken into account. To determine the equilibrium composition of a reacting mixture in both phases, chemical equilibrium constants as well as data concerning vapour-liquid equilibria for all components of the reaction mixture should be known. In the equilibrium state ... 

Fig. 7 Thermodynamic equilibrium compositions on dry basis for the steam reforming of ethanol. All species are in gas phase. Initial concentrations of CO, CH4, CH3CHO are taken as zero in the calculation.

The major activity in gas-phase studies now depends on the use of modem techniques such as ion cyclotron resonance (ICR). Thus, as already mentioned (Section ELD). Fujio, Mclver and Taft131 measured the gas-phase acidities, relative to phenol, of 38 meta- or para-substituted phenols by the ICR equilibrium constant method, and their results for +R substituents led them to suggest that such substituents in aqueous solution exerted solvation-assisted resonance effects. It was later163 shown by comparison of gas-phase acidities of phenols with acidities of phenols in solution in DMSO that solvation-assisted resonance effects could also occur even when the solvent did not have hydrogen-bond donor properties. Indeed for p-NC>2 and certain other substituents these effects appeared to be larger than in aqueous solution. 

CAe Molar concentration of A in liquid phase in equilibrium with partial pressure Pag in gas phase kmol/m3 NL-3... 

As an initial example of using DFT calculations to describe phase stability, we will continue our discussion of bulk metal oxides. In this chapter, we are interested in describing the thermodynamic stability of a metal, M, in equilibrium with gas-phase O2 at a specified pressure, Po2, and temperature, T. We will assume that we know a series of candidate crystal structures for the metal... 

Potential interferences in the measurement of nitric acid using this method include removal of gaseous HN03 on the Teflon particle filter and/or volatilization of particle nitrate collected on this Teflon filter. As discussed in Chapter 7, NH4N03 is a common particle component, but exists in equilibrium with gas-phase NH3 and HN03 ... 

This equation relies on the assumption that adsorbed oxygen on the electrode surfaces is in equilibrium with gas phase oxygen. This has lead to a number of applications of this type of cell as a sensor. The principle applications are listed below 4... 

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