Pure gaseous compound

We have discussed in some detail the various methods that can be used to obtain the standard Gibbs function of formation of a pure gaseous compound such as HCl(g). As many of its reactions are carried out in aqueous solution, it also is desirable to know AfGm for HCl(aq). 

In addition to the oxoacids, there are a small number of other acids, such as HC1, that do not contain oxygen. Although the pure, gaseous compound HC1 is named hydrogen chloride according to the rules for binary compounds, the aqueous solution is named hydrochloric acid, HCl(a ). This example is typical of non-oxygen-containing acids The prefix hydro- and the suffix -ic acid are used for the aqueous solution in such cases. 

The density of a pure gaseous compound was measured at 0.00°C as a function of pressure to give the following results ... 

A 0.109-gram sample of a pure gaseous compound occupies 112 mL at 100.°C and 750. torn What is the molecular weight of the compound ... 

Several molecular compounds have common names that you use every day, such as water, ammonia, and alcohol. But common names can cause confusion. Does ammonia mean ammonia the pure gaseous compound or a solution of ammonia in water, as it is sold in stores And, there are severed compounds known as alcohol. Clearly, a more accurate system of naming compounds is necessary. So here, and in Chapter 4, you can learn how compounds are named following the international rules of chemical nomenclature. The goal of nomenclature is to develop a name that gives all the necessary information to allow someone else to construct the formula of the compound, and vice versa. 

Since no specific compounds were included in this kind of representation, the group additivity (GA) thermoproperties [70] are used as inputs for computer programs that calculate at request the thermochemical properties for many pure gaseous compounds. Some programs are as follows ... 

The empirical formula of an organic compound can be obtained from its percentage composition by mass. For compounds that contain only carbon, hydrc en and oxygen this can be found in a quantitative combustion experiment in an excess of oxygen. The number of carbon atoms in an organic molecule can be calculated if the volume of carbon dioxide produced by complete combustion of a known volume of pure gaseous compound is measured (Chapter 1). 

All stable pure compounds have a triple point and a critical point. The critical point is the endpoint of the liquid-gas line in the phase diagram and the point where the liquid and gas phases become indistinguishable. Any gaseous compound becomes supercritical when compressed to a pressure higher than the critical pressure (Pc) above the critical temperature Cf ). Figure 2 shows photographs... 

In CVD, solids are formed from gaseous compounds. In chemical vapour transport, a solid or solids interact with a volatile compound and a solid product is deposited in a different part of the apparatus. It is used both for preparing compounds and for growing crystals from powders or less pure crystalline material. 

Let us now continue with our discussion of how to relate the chemical potential to measurable quantities. We have already seen that the chemical potential of a gaseous compound can be related to pressure. Since substances in both the liquid and solid phases also exert vapor pressures, Lewis reasoned that these pressures likewise reflected the escaping tendencies of these materials from their condensed phases (Fig. 3.9). He thereby extended this logic by defining the fugacities of pure liquids (including subcooled and superheated liquids, hence the subscript L ) and solids (subscript s ) as a function of their vapor pressures, pil ... 

The aqueous solubility of a gaseous compound is commonly reported for 1 bar (or 1 atm = 1.013 bar) partial pressure of the pure compound. One of the few exceptions is the solubility of 02 which is generally given for equilibrium with the gas at 0.21 bar, since this value is appropriate for the earth s atmosphere at sea level. As discussed in Chapter 3, the partial pressure of a compound in the gas phase (ideal gas) at equilibrium above a liquid solution is identical to the fugacity of the compound in the solution (see Fig. 3.9d). Therefore equating fugacity expressions for a compound in both the gas phase and an equilibrated aqueous solution phase, we have ... 

The existence of O (ads) species substantiates previous conclusions which indicated that these entities are determinant, once activated by photoproduced holes, in the initial oxidation step of pure gaseous or liquid organic compounds (refs 14,15). 

In contrast to conventional nematic liquid crystals, the molecular units are disk shaped and range widely in size, even when the mesophase is produced by the pyrolysis of pure organic compounds (17). Many of the molecules are volatile or reactive in the temperature range over which the mesophase is fluid, and the evolution of gaseous species usually causes the mesophase to be extensively deformed by bubble percolation before it congeals to a solid semicoke. 

How do we explain the low conductivity of these pure covalent compounds The atoms in each compound are held together by strong covalent bonds. Whether the compound is in the liquid, solid, or gaseous state, these bonds do not break. Thus, covalent compounds (unlike ionic compounds) do not break up into ions when they melt or boil. Instead, their atoms remain bonded together as molecules. For this reason, covalent compounds are also called molecular compounds. The molecules that make up a pure covalent compound cannot carry a current, even if the compound is in its liquid state or in solution. 

From the chemists point of view, however, water in its purest form does not exist in the environment It is very difficult and costly to produce and has anomalous solvent properties, so that it is contaminated immediately by dissolving trace elements or compounds from its environment. On the other hand, pure air is simply a mixture of several gaseous compounds of well-known composition. 

Thallium is obtained as a by-product of the recovery of lead and zinc. Gaseous compounds of the element formed during the recovery process are captured. They are then treated to obtain the pure metal. 

Silicon s most familiar use is in the production of microprocessor chips. Computer microprocessor chips are made from thin slices, or wafers, of a pure silicon crystal. The wafers are doped with elements such as boron, phosphorus, and arsenic to confer semiconducting properties on the silicon. A photographic process places patterns for several chips onto one wafer. Gaseous compounds of metals are allowed to diffuse into the open spots in the pattern, and then the pattern is removed. This process is repeated several times to build up complex microdevices on the surface of the wafer. When the wafer is finished and tested, it is cut into individual chips. 

Since the gaseous compounds can be purified very effectively the resulting fibers are very pure with transmission losses of < 5 db at a wavelength of 0,85 [im. 

IR measures the frequencies of molecular vibrations which depend on the masses of atoms and the force constants (i.e. the stiffness ) of chemical bonds (see Topic C8). Spectra can be measured for pure gaseous and liquid samples, but solids are usually measured by grinding them to make a mull with a heavy hydrocarbon liquid ( nujol ) which has relatively few, and well known, IR bands. Many types of chemical bond, such as C-H and C=0, give bands with characteristic IR frequencies and can thus be identified. In the case of compound X discussed above, bands appear which are characteristic of aromatic C-H bonds (suggesting a C6H6 benzene ring) and of C=0 groups bound to... 

Formaldehyde (CH20) is an important compound in the synthesis of various chemicals on an industrial scale. One of the first industrial applications was in the production of artificial Indigo. The variety of end products produced from formaldehyde include resins or glues (produced by the condensation of formaldehyde with urea, phenol, or melamine) as well as rubber, paper, fertilizers, explosives, engineering plastics, and specialty chemicals like acrolein, methacrylic acid, methyl methacrylate, etc. Because it is nearly impossible to handle in its pure gaseous form, formaldehyde is almost exclusively produced... 

Taking into account the fact that aqueous solutions of certain covalent compounds (notably bases that are not hydroxides, and acids) are electrolytes (while the pure covalent compounds, such as liquid sulfuric acid, gaseous hydrogen chloride, or gaseous ammonia, are not), the model accepts that during the dissolution process, the molecules of the solute are split into ions by reacting chemically with water. This process is called ionisation. It has been observed that electrolytes do not all ionise to the same extent. Some are almost completely ionised (strong electrolytes, for example sulfuric acid and hydrochloric acid ) while others are feebly ionised (weak electrolytes, for example acetic acid and the base ammonia). 

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