Gases, gaseous substances

It is a requirement of the Gas Act 1986, Schedule 5, that where air at high pressure or any gaseous substance... 

All gas mixtures are homogeneous hence all gas mixtures are solutions. Air is an example. There is only one phase—the gas phase—and all the molecules, regardless of the source, behave as gas molecules. The molecules themselves may have come from gaseous substances, liquid substances, or solid substances. Whatever the source of the constituents, this gaseous solution, air, is a single, homogeneous phase. As with other solutions, the constituents of air are separated by phase changes. 

Reaction enthalpies can be estimated by using mean bond enthalpies to determine the total energy required to break the reactant bonds and form the product bonds. In practice, only the bonds that change are treated. Because bond enthalpies refer to gaseous substances, to use the tabulated values, all substances must be gases or converted into the gas phase. 

Sllf-Tfst 9.9B Hydrogen chloride gas is added to a reaction vessel containing solid iodine until its partial pressure reaches 0.012 bar. At the temperature of the experiment, K = 3.5 X 10-32 for 2 HCl(g) + I2(s) 2 HI(g) + Cl2(g). Assume that some 12 remains at equilibrium. What are the equilibrium partial pressures of each gaseous substance in the reaction mixture ... 

All living organisms require at least one mobile phase (gas or liquid) in order to exist. Life on Earth as we know it would be impossible without the involvement of the liquid phase of water. The gas phase is necessary for life forms that consume gaseous substances or that produce gaseous waste products. Hence, the very functioning of the biosphere implicitly depends on the existence of the mobile atmosphere and hydrosphere, both of which are in... 

In general, liquids have lower entropies than gases, since the molecules of gas have much more freedom and randomness. Solids, of course, have still lower entropies. Any reaction in which the reactants are all liquids and one or more of the products is a gas is therefore thermodynamically favored by the increased entropy the equilibrium constant for that reaction will be higher than it would otherwise be. Similarly, the entropy of a gaseous substance is higher than that of the same substance dissolved in a solvent. 

After a rainfall, puddles of water slowly disappear. The higher the temperature, the faster the puddles vanish. Puddles disappear because water molecules move from the liquid phase to the gas phase through evaporation. Evaporation is common to all substances in condensed phases, not Just to water. We use the term vapor to describe a gaseous substance that forms by evaporation. Evaporation from bodies of water guarantees that the Earth s atmosphere always contains water vapor. 

The experimental study of combustion made by Lavoisier proved the correctness of that part of Stahl s phlogistic theory which asserted that all processes of combustion are very similar, but also proved that this likeness consists in the combination of a distinct gaseous substance with the material undergoing combustion, and not in the escape therefrom of the Principle of fire, as asserted by the theory of Stahl. After about the year 1790, it was necessary to think of combustions in the air as combinations of a particular gas, or air, with the burning substances, or some portions of them. 

Gas Cleaning and Purification. Gas cleaning means the removal of impurities existing in the form of suspended liquid or solid particles, such as vapors, mist, fog, smog, smoke or dust. The impurities might also include gaseous substances that are objectionable or obnoxious, and their removal is usually called purification... 

Gas, Combustible. Any gaseous substance or mixture consisting principally of carbon and hydrogen contg gases used for illuminating or heating purposes may be called combustible gas. These include blast furnace gas, carbon monoxide gas, coal gas, coke-oven gas, fuel gas, natural gas, oil gas, producer gas, tar gas, water gas and wood gas... 

The most common analytical methods used were gas chromatography, HPLC, AA spectrophotometry, polarography, colorimetry, and potentiometry with ion-selective electrodes. In this study GC/MS and other more expensive instrumentation were avoided. If sorbent tubes could not be used for gaseous substances, then the less desirable miniature bubblers or impingers were considered. Although these devices are inconvenient they were often used because no better alternatives were available. Bags were used in a few cases where the analyte could not be retained on a sorbent because of volatility and a small tendency to sorb. Filters were used for particulates. Combinations of collection devices were used if we felt that both particulates and vapor might be present in the analyte. 

Indeed, this interdependence of all but a small number of independent properties ( degrees of freedom ) is observed to be one of the most striking and universal features of all known gaseous substances. If we consider a fixed quantity of a pure substance ( simple gas ) in the... 

Molecular compounds consist of two or more stable species held together by weak forces. In clathrittes-, a gaseous substance, such as SO . HC1. CO.-, or n rare gas is held in the crystal lattice of a solid, such as beta-quinol. by Van der Waals-London dispersion forces. The gas hydrates, e.g.. CU- 6H 0. contain halogen molecules similarly trapped in ice-like... 

Let us examine one more simple three-step mechanism whose steady-state characteristics are also of the hysteresis type. In what follows we will show that their type differs considerably from the previous one. It is the mechanism including steps of "consecutive adsorption one gas-phase substance is adsorbed on unoccupied sites and is then joined by a second gaseous substance, whereupon the two intermediates interact. In the general form this... 

For the standard state of gaseous substances, we want to calculate thermodynamic properties in the 1.0-bar ideal gas state from measured values of properties at the measurement pressure, P. The calculation consists of the following three steps ... 

With = 0, pq = 0, and - -1.3 kJ -mol-1 found in chemical handbooks, we then obtain the standard affinity equal to A0 = -/% = 1.3 kJ - mol-1. If the gas phase is an ideal gas, the activities are equal to the molar fraction of gaseous substances. Further, if solid I2is a pure substance, the activity of I2 is unity. The equilibrium constant K in the standard state will then be expressed by the molar fractions of gaseous constituents as shown in Eq. 6.9 ... 

A gaseous substance at dilute density normally is in the state of an ideal gas and it turns into a non-ideal gas as the density increases. A further increase in the density leads to the condensation of a gas into a liquid or solid phase. In the ideal gaseous state the chemical potential of a substance changes linearly with the logarithm of the density, and a deviation from the linearity occurs in the non-ideal state. For a condensed substance in the liquid or solid state its chemical potential hardly changes with the density. This chapter concerns the equations of state and the calculation of thermodynamic potentials of gaseous and condensed substances. 

To find the molecular weight of any gaseous substance it is necessary therefore only to find the weight in grams of 22.4 liters of the gas under standard conditions. In actual practice it is not convenient to weigh containers which hold 22.4 liters. It is only necessary to know the weight of any volume and the conditions of the experiment. From these data the molecular weight can be calculated. 

The development of the chemistry of the atmosphere was somewhat delayed by the early lack of realisation that there exist various kinds of gases. At first the term air was applied to all gaseous substances, and not until the commencement of the seventeenth century was the difference m the nature of various gases recognised at this time van Helmont, who introduced the term gas, observed the divergence in the properties of gases from different sources, and as an almost immediate result carbon dioxide was accepted as a minor constituent of the atmosphere. 

As an index for toxicity of gaseous substances, the median lethal concentration (LC 5 0 ) and the threshold limit value (TLV) are used to evaluate acute toxicity. LCso is the gas concentration (ppm) in air which results in the death of 50% of a population of test animals by inhalation. TLV is the threshold limit of exposure which does not cause any serious sickness in workers under normal conditions of an 8 hours day and a 40-48 hour work week. TLV is usually given in combination with the time-weighted-average concentrations for 8 hours per day (TLV—TWA), or with the short time exposure limit (TLV-STEL), which is that exposure which should not be exceeded even for a relatively short period (15-30 minutes), or with the ultimate limit (TLV-C), which defines the exposure level that should not be exceeded under any circumstances. 

For a gas phase. The standard state for a gaseous substance, whether pure or in a gaseous mixture, is the (hypothetical) state of the pure substance B in the gaseous phase at the standard pressure p = p and exhibiting ideal gas behaviour. The standard chemical potential is defined as... 

M. Gay-Lussac has shown in an interesting Memoir that gases always unite in a very simple proportion by volume, and that when the results of the union is a gas, its volume also is very simply related to those (volumes) of its components. But the proportions of weight of substances in compounds only seem to depend on the relative number of molecules which combine, and on the number of compound molecules which result. It must then be admitted that very simple relations also exist between the volumes of gaseous substances and the numbers of simple or compound molecules which form from them. The first hypothesis to present itself in this connection, and apparently even the only admissible one, is the supposition that the number of integral molecules in any gas is always the same for equal volumes, or always proportional to the volumes. 

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