Solubility of a gas

Henry s Law. The solubility of a gas is directly proportional to the partial pressure exerted by the gas ... 

In order to define completely the solubility of a gas in a liquid, it generally is necessary to state the temperature, the equilibrium partial pressure of the solute gas in the gas phase, and the concentration of the solute gas in the liquid phase. Stric tly speaking, the total pressure on the system also should be stated, but for low total pressures, less than about 507 kPa (5 atm), the solubihty for a particular partial pressure of solute gas normally will be relatively independent of the total pressure of the system. 

Plasticization Gas solubility in the membrane is one of the factors governing its permeation, but the other factor, diffusivity, is not always independent of solubility. If the solubility of a gas in a polymer is too high, plasticization and swelhng result, and the critical structure that controls diffusion selectivity is disrupted. These effects are particularly troublesome with condensable gases, and are most often noticed when the partial pressure of CO9 or H9S is high. H9 and He do not show this effect This problem is well known, but its manifestation is not always immediate. 

General description. Porosity refers to cavities formed within the weld metal during the solidification process. Such cavities may form due to decreased solubility of a gas as the molten weld metal cools or due to gas-producing chemical reactions within the weld metal itself. At times, cavities can form a continuous channel through the weld metal (worm holes, piping), resulting in leaks (Case History 15.3). 

Then solubility of a gas in the liquid on a weight basis is given by the equation as follows ... 

The solubility of a gas generally decreases with any increase in temperature. So, if a solution in a closed receptacle is heated above the filling temperature during transport or storage, loss of gas can result on opening or liquid discharge. 

Pressure has a major effect on solubility only for gas-liquid systems. At a given temperature, raising the pressure increases the solubility of a gas. Indeed, at low to moderate pressures, gas solubility is directly proportional to pressure (Figure 10.5b). 

Thus we see that the equilibrium solubility of a gas again involves a balance between randomness and energy as it does for a solid, but the effects are opposite. For a gas, the tendency toward maximum randomness favors the gas phase, opposing dissolving. The tendency toward minimum energy favors the liquid state, hence favors dissolving. 

Raising the temperature always tends to favor the more random state. This means that less gas will dissolve, since the gas is more random than the liquid. The solubility of a gas decreases as temperature is raised. 

The straight lines in Fig. 8.21 show that the solubility of a gas is directly proportional to its partial pressure, P. This observation was first made in 1801 by the English chemist William Henry and is now known as Henry s law. The law is normally written... 

EXAMPLE 8.4 Sample exercise Estimating the solubility of a gas in a liquid... 

The solubility of a gas is proportional to its partial pressure, because an increase in pressure corresponds to an increase in the rate at which gas molecules strike the surface of the solvent. 

Henry s law The solubility of a gas in a liquid is proportional to its partial pressure above the liquid solubility X partial pressure. hertz (Hz) The SI unit of frequency 1 Hz is one complete cycle per second 1 Hz = l s 1. 

The solubility of a gas generally decreases with any increase in temperature. 

Unlike solids for which solubility in a liquid generally increases with increasing temperature, the solubility of a gas in a liquid usually decreases as the temperature increases. Knowing this, explain why you should never heat a can containing a carbonated soft drink. 

The solubility of nearly all gases in water decreases as the temperature is increased. Furthermore, the solubility of a gas increases with the partial pressure of the gas above the surface of a liquid solution, expressed as Henry s Law ... 

The equilibrium adsorption characteristics of gas or vapor on a solid resemble in many ways the equilibrium solubility of a gas in a liquid. Adsorption equilibrium data are usually portrayed by isotherms lines of constant temperature on a plot of adsorbate equilibrium partial pressure versus adsorbent loading in mass of adsorbate per mass of adsorbent. Isotherms take many shapes, including concave upward and downward, and S-curves. Equilibrium data for a given adsorbate-adsorbent system cannot generally be extrapolated to other systems with any degree of accuracy. 

Some of these factors were addressed in the Reactions and Periodicity chapter. In general, the solubility of a solid or liquid will increase with temperature and be unaffected by pressure changes. The solubility of a gas will decrease with increasing temperature and will increase with increasing partial pressure of the gas (Henry s law). 

Henry s law The solubility of a gas will increase with increasing partial pressure of the gas. 

Whilst the solubility of a gas is not substantially affected by the total pressure in the system for pressures up to about 500 kN/m2, it is important to note that the solubility falls with a rise of temperature. Thus, for a concentration of 25 per cent by mass of ammonia in water, the equilibrium partial pressure of the ammonia is 30.3 kN/m2 at 293 K and 46.9 kN/m2 at 303 K. 

Generally, the higher the pressure, the higher is the solubility of a gas in a liquid. This relationship is expressed quantitatively by Henry s Law which states that the mass of gas (m) dissolved by a given volume of solvent at a constant temperature is proportional to the gas pressure (p) with which it is in equilibrium ... 

Ostwald coefficient physchem A measure of the solubility of a gas in a liquid, equal to the volume of gas that can be dissolved in a given volume of liquid divided by the volume of liquid. ast.valt, ko-3,fish-ant ... 

Henry s Law The solubility of a gas in an aqueous solution is directly proportional to its atmospheric partial pressure. The constant of proportionality is a function of temperature and the ionic strength of the solution. 

Salting out A decrease in the solubility of a gas or solute with increasing ionic strength of the solution. 

Another factor that differentiates the solubility of gases from solids and liquids is the effect of pressure. The effect of pressure on gas solubility was studied extensively by a contemporary and close associate of John Dalton named William Henry (1775-1836). Henry s Law states that the solubility of a gas is directly proportional to the partial pressure of that gas over the solution. Stated mathematically, Henry s Law is c = kP, where c is the concentration of the dissolved gas in moles per liter, k is Henry s law constant for the solution, and P is the partial pressure of the gas above the solution. Henry s Law is demonstrated every time a carbonated beverage is opened. During the carbonation process, carbon dioxide is dis-... 

Compciring gas solubility in liquids with the concept of vapor pressure highlights another important pattern Increasing pressure increases the solubility of a gas in liquid. Just as high pressures make it more difficult for surface-dwelling liquid molecules to escape into vapor phase, high pressures inhibit the escape of gases dissolved in solvent. Henry s law summarizes this relationship between pressure and gas solubility ... 

Equations 6.11 and 6.12 lead to a very important concept. When the solubility of a gas into a liquid is very poor (i.e., m is very large), the second term of Equation 6.12 is negligibly small compared to the third term. In such a case, where the liquid-phase resistance is controlling,... 

The solubility of a gas is an integral part for the prediction of the permeation properties. Various models for the prediction of the solubility of gases in elastomeric polymers have been evaluated (57). Only a few models have been found to be suitable for predictive calculations. For this reason, a new model has been developed. This model is based on the entropic free volume activity coefficient model in combination with Hildebrand solubility parameters, which is commonly used for the theory of regular solutions. It has been demonstrated that mostly good results are obtained. An exception... 

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