Homogeneous equilibria, gaseous

Expressions for homogeneous equilibria Gaseous hydrogen iodide is produced by the equilibrium reaction of hydrogen gas with iodine. Iodine and some of its compounds have important uses in medicine, as illustrated in Figure 17.7. How would you write the equilibrium constant expression for this reaction in which hydrogen and iodine react to form hydrogen iodide ... 

The purpose of this chapter is to outline the simplest methods of arriving at a description of the distribution of species in mixtures of liquids, gases and solids. Homogeneous equilibrium deals with single phase systems, such as electrolyte solutions (e.g., seawater) or gas mixtures (e.g., a volcanic gas). Heterogeneous equilibrium involves coexisting gaseous, liquid and solid phases. 

We are going to consider three types of equilibrium gaseous phase homogeneous, liquid phase homogenous and solid phase homogenous equilibria. 

In the reactions described so far, all the reactants and products have been gaseous the equilibrium systems are homogeneous. In certain reactions, at least one of the substances involved is a pure liquid or solid the others are gases. Such a system is heterogeneous, because more than one phase is present. Examples include... 

As for Allende s inclusions, variable contributions of a component produced in neutron-rich nuclear statistical equilibrium best explains the Ti- Ca data. Some parts of the solar nebula were depleted in these isotopes as deficits are also seen. There are several possibilities for explaining the variations in Ti. 1) The neutron-rich component itself may be heterogeneous and incorporate locally less neutron-rich statistical equilibrium products (Hartmann et al. 1985). 2) Ti may result from another process like explosive Si or He burning (Clayton 1988). This component would be associated with the neutron-rich component but not completely homogenized. In all cases, carriers are solid grains which may have behaved differently than the gaseous nebula during the formation of the solar system. A minimum number of components may be calculated to account for the Ca and Ti isotopic data, which number up to 3 (Ireland 1990) but to be conservative at the 5ct level, clearly resolved effects are present only on 3 isotopes ( Ca, Ti, Ti). 

This equation is valid for a homogeneous state of equilibrium. For slow reactions, it is reasonable to assume that the chemical process is proceeding through states that are in thermomechanical equilibrium at all times, although chemical equilibrium is not established. This assumption is supported by the fact that, for example, for a gaseous mixture, collisions not causing reactions are far more frequent than collisions that cause reactions. At a specified... 

There are numerous possibilities for using equation (29) in conjunction with interface or gas-phase conditions to determine both m and T-. For example, the condensed product of equation (14) conceivably might experience the rate process of equation (1) as soon as Y = 1, so that equations (6) and (29) become two independent expressions for m and 7]. Alternatively and somewhat less unlikely, surface equilibrium may occur so that equation (12) determines T- in equation (29) in this case, a gas-phase analysis is generally needed to find Pi, j. It appears that in most real homogeneous propellants, the products of the exothermic condensed-phase reactions are mainly gaseous, so that considerations of dispersion or possibly of gas-phase reactions are most relevant for determining in equation (29), and equations (6), (11), or (12) are not directly useful. 

Equilibrium in gases. Applications. In dealing with applications, we come now to the methods by which we may determine the quantity of each substance present in a gaseous mixture in the state of chemical equilibrium, or more generally in any homogeneous mixture. Two ways are open. 

Variations of the dendty of perchloride of phosphorus vapor.— We have not applied as yet formula (3) to equilibrium phenomena which may be produced in homogeneous gaseous S3rstems. 

We briefly extend the preceding discussion to systems in which one or more pure condensed phases coexist with an ideal homogeneous mixture in gaseous, liquid, or solid form. It is now expedient to distinguish between pure condensed phases, subscript 5, and species involved in the solution, subscript i. For the reaction, written as -f- v,-A,- = 0 we write out the equilibrium condition as... 

A catalyst is a substance that increases the rate at which a chemical reaction approaches equilibrium without, itself, becoming permanently involved in the reaction. The key word in this definition is permanently since there is ample evidence showing that the catalyst and the reactants interact before a reaction can take place. The product of this interaction is a reactive intermediate from which the products are formed. This substratexatalyst interaction can take place homogeneously with both the reactants and the catalyst in the same phase, usually the liquid, or it can occur at the interface between two phases. These heterogeneously catalyzed reactions generally utilize a solid catalyst with the interaction taking place at either the gas/solid or liquid/solid interface. Additional phase transport problems can arise when a gaseous reactant is also present in the liquid/solid system. 

In later chapters (X and XIV) we shall give examples of the application of the Nernst theorem to the calculation of homogeneous and heterogeneous equilibrium constants. We shall also see (chap. X, 3) how the entropies of simple gaseous molecules may be calculated by statistical methods. 

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