Gases or Solutions

4 Oxidation Reactions Applicable for the Removal of PH3 from Gases or Solutions 

The oxidation reactions presented in this section in most cases are used to remove less than 1 vol% of PH3 from gases like N2, C2H2, or their mixtures. Earlier results are described in Phosphor B, 1964, pp. 58/9. For the removal of PH3 by physical or other chemical methods, see Section 1.3.1.3.13, pp. 138/41. The oxidation of diluted PH3 by metal complexes and free or bound oxygen, mostly for the removal from gases, was reviewed. Kinetics and mechanisms were discussed for most of these reactions [1]. 

The oxidation of PH3 by NOg in concentrated H2SO4 yields H3PO4 and NO which is partly reduced to NgO by PH3. The rate of this reaction also increases with increasing concentration of Cl , Br , or I [66, pp. 91/7]. 

With Ce and V Compounds. The oxidation of PH3 in C2H2/N2 mixtures by acidic Ce solutions with formation of H3PO4 and Ce takes place at an acceptable rate only in the presence of KBr [75] or KI [75, 76]. The oxidation of PH3 in low concentration by oxygen complexes of V supported on silica gel in the presence of KI and HCIO4 was investigated in [77]. 

With Compounds of Ni , Pd , and Pt. The removal of PH3 from inert gases with nickel oxide on activated carbon [113] and with Pd chloro complexes on kieselguhr [114] was described. Acidic solutions of H2PtCl6 oxidize PH3 to H3PO4 with formation of Pt which activates PH3 [115]. The rate of the reaction increases with increasing acidity of the solution and with increasing concentration of Cl , Br , I [23, pp. 305/7], or SCN [116]. 

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There are significant differences between the kinetic models for reactions carried out in the solid phase and those taking place in gases or solutions. Therefore, it is appropriate to describe briefly some of the kinetic models that have been found to be particularly applicable to reactions in inorganic solids. 

A number of other laser spectroscopic techniques are of interest but space does not permit their discussion. A few specialized methods of detecting laser absorption worthy of mention include multiphoton ionization/mass spectrometry (28), which is extremely sensitive as well as mass selective for gas-phase systems optically detected magnetic resonance (29) laser intracavity absorption, which can be extremely sensitive and is applicable to gases or solutions (30) thermal blooming, which is also applicable to very weak absorbances in gases or liquids (31) and... 

Process streams occasionally contain one substance, but more often they consist of mixtures of liquids or gases, or solutions of one or more solutes in a liquid solvent. 

Similarly the parent problem for fluorescence of phosphorescence emission in dilute gases or solution is the influence of coupling to foreign molecules on spontaneous emission [189]. The emission rate for an isolated molecule A is given by the Einstein A coefficient,... 

Zero-order reactions can be explained in two ways. In a process that is truly zero order with respect to all reactants (and catalysts, in the case of enzymes), either the activation energy is zero or every molecule has sufficient energy to overcome the activation barrier. This kind of reaction is rare in homogeneous reactions in gases or solutions. 

There is one special case to be noted Suppose we start with substances at unit concentration and end with substances also at unit concentration (z e i mole of each per liter, which would hold equally for gases or solutions, or, say, at i atmosphere pressure of each, which would apply to gases only), then the arbitiary concentration terms are each unity, and since the log of unity is zero, the expression for the affinity becomes—... 

In any reversible reaction involving gases or solutions that can be written... 

Metal oxide surfaces react with gases or solutions and they can be used as active phases, or as supports for catalysts. The behaviour of metal oxide surfaces is controlled by ... 

Since, under proper conditions, gases or solutes from liquid... 

Both kinds of quantity are needed if the yield of a chemical reaction is to be calculated under any particular conditons. Standard thermodynamic functions lead to standard equilibrium constants. Except at infinite dilution for gases or solutions, a condition of little importance in chemical industry, the properties of real mixtures are needed to calculate the yield from the standard equilibrium constant. No Haber-process chemist would keep his job for long who calculated the yield at 50 or 100 MPa from the standard equilibrium constant. Nor do we have even for mixtures of nitrogen + hydrogen + ammonia measured values of the properties needed. 

Keep in mind that we have assumed that the A S and A V from the tables are unchanged at all temperatures and pressures, that is, that they are constants. This is quite a good approximation for a reaction involving only solid phases such as this one, but you would not use it for reactions involving liquids, gases, or solutes. In general, all thermodynamic parameters do vary with T and P, so phase boundaries are in principle curved and not straight as we have assumed. However, the amount of curvature is quite small in some cases, such as this one. 

Samples to be studied in the ultraviolet or visible region are usually gases or solutions and are put in cells known as cuvettes. Spectra of gases are taken using enclosed cells, with an evacuated cell as a reference. Standard path-length of gas cells is usually 1 mm but cells with path-length of 0.1 to 100 mm are available for special cases. Sometimes spectra of solids may be taken directly. For this purpose, the solids are generally in the form of pellets. The pellets are kept in pellet holders for absorption measurements. 

More generally, for the components belonging to a phase with multiple components (mixtures of gases or solutions), the Ellingham curve delimits domains of predominance, whereas for components in a pure phase, the Ellingham curve delimits domains of existence. 

The presentations in the prior chapters have been limited to ideal systems, either gases or solutions. We now extend the thermodynamic and stochastic theory to non-ideal systems. 

Adding more information to equations Reactants and products may be solids, liquids, gases or solutions. You can show their states by adding state symbols to the equations. The state symbols are ... 

The equilibrium constant expression contains only partial pressures or concentrations of reactants and products that exist as gases or solutes dissolved in solution. Pure liquids and solids are not included in the expression for the equilibrium constant. 

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