Chemical reactions involving gases

Consider the special case for which the chemical reaction involves oxidation of a metal  

This chapter has provided a summary of the laws of thermodynamics and the important defined functions and relationships for applying these laws. The remainder of this book will focus on the way these laws and relationships are influenced by surfaces and interfaces. 

---

To proceed fiirther, to evaluate the standard free energy AG , we need infonnation (experimental or theoretical) about the particular reaction. One source of infonnation is the equilibrium constant for a chemical reaction involving gases. Previous sections have shown how the chemical potential for a species in a gaseous mixture or in a dilute solution (and the corresponding activities) can be defined and measured. Thus, if one can detennine (by some kind of analysis)... 

Chemical reactions involving gases carried out in closed containers resemble in many ways the H20(/)-H20(g) system. The reactions are reversible reactants are not completely consumed. Instead, an equilibrium mixture containing both products and reactants is obtained. At equilibrium, forward and reverse reactions take place at the same rate. As a result, the amounts of all species at equilibrium remain constant with time. 

Many chemical reactions involve gases. By assuming ideal behavior for these gases, we can carry out stoichiometric calculations if the pressure, volume, and temperature of the gases are known. 

The law of combining gas volumes states that in chemical reactions involving gases, the ratio of the gas volumes is a small whole number. 

In chemical reactions involving gases, the amounts of some reactants or products may be specified in units of mass. These problems are solved by the same methods as in Chapter 4, except that the number of moles of gas may be determined from its volume, temperature, and pressure using the ideal gas law. As alway we turn to the balanced equation for the relative numbers of moles of all reactants and products. 

Even in this brief overview, we see that a single pollutant—NO2 in this case—can have a complex impact on the air around us. We also see that the effects of various pollutants can be coupled in unexpected ways the simultaneous presence of NO2 and VOCs leads to the generation of O3, another of the criteria pollutants. Clearly, the chemistry of air pollution is quite complex, so we will not be able to delve into many aspects of it in great detail. But it should be clear that to improve our understanding of these important issues, we must first explore the properties of gases, gas mixtures, and chemical reactions involving gases. 

Primary particles, such as road dust, salt (sea-) spray from the oceans and cement dust do not change form after emission, whereas a substantial fraction of mass of the secondary particles, such as photochemically produced sulfates and photochemical smog, is formed by in situ chemical reactions involving gases. 

Some chemical reactions involving gases are performed in sealed glass tubes that do not melt at high temperatures. The tubes have thin walls and can easily break. Use the kinetic theory of gases to explain why the tubes should not be heated to high temperatures. 

The ideal gas equation relates the number of moles of gas to the physical properties of that gas. When a chemical reaction involves a gas, the ideal gas equation provides the link between P-V-T data and molar amounts. 

In eadi specific case the choice of an adsorbent, electrophysical parameters and the method of registration of its change as well as the choice of various pre-adsorption treatment techniques of the surface of adsorbent is dictated by the type and nature of analytical problem to be solved. For instance, if particles active from the standpoint of the change in electrophysical parameters of semiconductor adsorbent occur on the surface of the latter due to development of a chemical reaction involving active particles, it is natural to use either semiconductor material catalyzing the reaction in question or if this is not possible specific surface dopes accelerating the reaction. Above substances are used as operational element of the sensor. If such particles occur as a result of adsorption from adjacent volume, one can use semiconductor materials with maximum adsorption sensitivity to the chosen electrophysical parameter with respect to a specific gas as operational element. 

Theory The official process is a development of the Gutzeit Test wherein all arsenic present is duly converted into arsine gas (AsH3) by subjecting it to reduction with zinc and hydrochloric acid. Further, it depends upon the fact that when arsine comes into contact with dry paper permeated with mercuric (Hg2+) chloride it produces a yellow strain, the intensity of which is directly proportional to the quantity of arsenic present. The various chemical reactions involved may be expressed by the following equations ... 

Even less expected, perhaps, are the reactions involving gas-solid addition of HBr, Cl2, and Br2 to a, 3-unsaturated acid guest species in a- and P-cyclodextrin inclusion complexes (242). Although the chemical yields are not high, the optical yields in some cases are extraordinary. Thus, chlorine addition to methacrylic acid in a-cyclodextrin yields (- )-2,3-dichloro-2-methylpropanoic acid in nearly quantitative optical yield. The 3-cyclodextrin methacrylic acid clathrate undergoes chlorine addition to yield preferentially the enantiomeric (+ )-product, with an e.e. of 80%. 

In particular, chemists observed that nickel could bond with carbon monoxide. The resulting compound, nickel tetracarbonyl, Ni(C0)4, is a gas. At the time, the nature of the bonding in this compound was unexplainable. Even so, chemists could easily produce and decompose Ni(C0)4. The chemical reactions involved were used to purify nickel, and led to the establishment of a company that later became International Nickel Company, INCO. 

In summary, gas-phase reactions between aldehydes and NOj occur readily and with strong exothermicity. The rate of reaction is largely dependent on the alde-hyde/N02 mixture ratio, and is increased with increasing NO2 concentration for aldehyde-rich mixtures. On the other hand, no appreciable gas-phase reactions involving NO are likely to occur below 1200 K. The overall chemical reaction involving NO appears to be third order, which impUes that it is sensitive to pressure. The reactions discussed above are important in understanding the gas-phase reaction mechanisms of nitropolymer propellants. 

On an industrial scale, chemical reactions involving reactants in the gaseous or vaporised state which come into contact with a solid, which is either a catalyst or another reactant, necessarily involve several physical and chemical steps. Some of these physical and chemical steps are coupled and it is this complexity, together with the problem of efficient gas—solid contact, which dictates that gas—solid catalytic and non-catcilytic reactions should be considered as a particular class of problem. 

When the vapour of alkali metals is mixed at low pressures, of the order 10 3mm., with certain halogen compounds, a cold, highly diluted flame is produced. A deposit of alkali halide is formed on the wall of the tube in which the reaction takes place, and from the distribution of this deposit and the velocity of the gas stream the partial pressures of the reacting substances and the reaction velocity can be inferred. A number of investigations with various modifications of this method have been carried out by Polanyi and others, J and a careful analysis and interpretation of the results has yielded much interesting and valuable information about the speed of the chemical reactions involved. 

Particles Catalyze a Chemical Reaction Involving the Absorbed Gas Phase Component... 

This second definition is useful when ion and electron movement is involved in chemical reactions. Chemical reactions involving ionic compounds are best interpreted by this definition. Consider the attack of dilute hydrochloric acid on metallic zinc. The zinc dissolves and forms zinc chloride solution and the hydrogen gas fizzes off ... 

FIGURE 1 The workhorses in the chemical industry for heterogeneously catalyzed reactions involving gas/liquid reactants. 

Reactions involving gas, liquid, and solid are often encountered in the chemical process industry. The most common occurrence of this type of reaction is in hydroprocessing operations, in which a variety of reactions between hydrogen, an oil phase, and a catalyst have been examined. Other common three-phase catalytic reactions are oxidation and hydration reactions. Some three-phase reactions, such as coal liquefaction, involve a solid reactant. These and numerous other similar gas-liquid solid reactions, as well as a large number of gas-liquid reactions, are carried out in a vessel or a reactor which contains all three phases simultaneously. The subject of this monograph is the design of such gas-liquid -solid reactors. 

However, despite the complexity of this scheme much valuable information has been obtained by applying some simplified analysis. In all these cases a major problem that has been considered, and to a large extent solved, is concerned with the combustion mechanism of individual droplets that make up the spray. In particular it has been necessary to study the nature of the combustion process and whether combustion occurs in the gas phase or on the surface of the droplet and whether the rate is controlled by vaporization or by the kinetics of the chemical reactions involved. 

In the chemical vapor deposition (CVD) process, heat is supplied through resistive heating, infrared heating, laser beam or plasma to effect a gas-phase chemical reaction involving a metal complex. The metal produced from the reaction deposits by nucleation and growth on the hot substrate which is placed in the CVD reactor. Effective reactants... 

---