Partial pressure, of a gas

Increasing or decreasing the partial pressure of a gas is the same as increasing or decreasing its concentration. The effect on a reaction s equilibrium position can be analyzed as described in the preceding example for aqueous solutes. Since the concentration of a gas depends on its partial pressure, and not on the total pressure of the system, adding or removing an inert gas has no effect on the equilibrium position of a gas-phase reaction. 

ED q, narcotic potency, is expressed as the partial pressure of a gas in breathing mixtures requited to produce a certain degree of anesthesia in 50% of the test animals. 

This remarkably simple relationship is depicted in Figure 14. It was apparent from his results that the volume fraction of the solvent determined the probability of interaction with the solute in much the same way that the partial pressure of a gas determines the probability of collision. It also indicated that the influence of each stationary phase component was independent and unaffected by presence of the other. 

Next to sales contract specifications, coiTosion protection ranks highest among the reasons for the removal of acid gases. The partial pressure ol the acid gases may be used as a measure to determine whether treatment IS required. The partial pressure of a gas is defined as the total pressure of the system times the mole % of the ga,seous component. Where ( 02 is present with free water, a partial pres.sure ot. hi psia or greater would indicate that CO2 corrosion should be expected. If CO2 is not removed, inhibition and special metallurgy may be required. Below 15 psia, COt corrosion is not normally a problem, although inhibition may be required. 

In other words, the partial pressure of a gas in a mixture is equal to its mole fraction multiplied by die total pressure. This relation is commonly used to calculate partial pressures of gases in a mixture when the total pressure and the composition of the mixture are known (Example 5.9). 

Our task is to find the relation between the partial pressure of a gas and its mole fraction. 

To find the relation between the partial pressure of a gas in a mixture and its mole fraction, we first express the partial pressure, Pa, of a gas A in terms of the amount of A molecules present, wA, the volume, V, occupied by the mixture, and the temperature, T ... 

The relation that we have derived for the partial pressure of a gas A is... 

The partial pressure of a gas is the pressure that it would exert if it were alone in the container the total pressure of a mixture of gases is tire sunt of the partial pressures of the components the partial pressure of a gas is related to the total pressure by the mole fraction PA = xAP. 

It is important to realize that the assumption of a rate-determining step limits the scope of our description. As with the steady state approximation, it is not possible to describe transients in the quasi-equilibrium model. In addition, the rate-determining step in the mechanism might shift to a different step if the reaction conditions change, e.g. if the partial pressure of a gas changes markedly. For a surface science study of the reaction A -i- B in an ultrahigh vacuum chamber with a single crystal as the catalyst, the partial pressures of A and B may be so small that the rates of adsorption become smaller than the rate of the surface reaction. 

According to Dalton s law, the partial pressure of a gas (Pgas) is equal to its fractional concentration (% total gas) multiplied by the total pressure (Ptot) of all gases in a mixture ... 

A few gases may be involved in some enzyme reactions, e.g., C02 and 02 as used by carbonic anhydrase and produced by catalase, respectively. If the presence of such dissolved gases affects rates and equilibria at ordinary pressure, their importance will increase at higher pressure. Henry s law says that the partial pressure of a gas above a solution is proportional to its mole fraction in the solution. At high pressure it is more correct to speak of the fugacity / of a gas, instead of partial pressure, in the same sense that one uses activity instead of concentration in solution calculations. In dilute solutions, the fugacity of the dissolved gas is given by... 

Henry s law The partial pressure of a gas in equilibrium with gas dissolved in a solution is proportional to the concentration of dissolved gas P = Hdissolved gas]. The constant k is called the Henry s law constant. It is a function of the gas, the liquid, and the temperature, hertz. Hz Unit of frequency, s-1. heterogeneous Not uniform throughout. 

According to Dalton s law of partial pressures (see p 163), the partial pressure of a gas in a mixture is given by the product of its volume fraction and the total pressure. Therefore the equilibrium pressure of each gas is... 

The constant kH, which is called Henry s constant, depends on the gas, the solvent, and the temperature (Table 8.5). The law implies that, at constant temperature, doubling the partial pressure of a gas doubles its solubility. 

In order to calculate the concentration loss, according to Equation (3.77), a relationship between partial pressure of a gas species at the reaction zone and at the bulk is required. This relationship is provided by the equations regulating mass transport in porous media, as defined in Section 3.3.2. 

The partial pressure of a gas in a gas mixture, whether such a mixture is ideal or real, is defined by... 

Oxygen dissolves in water according to Henry s law, The partial pressure of a gas in a liquid is equal to the partial pressure of the gas above the liquid. Therefore, the DO concentrations depend on the atmospheric pressure. They are also temperature-dependent as the solubility of gases decreases with increasing temperature. Another factor that decreases the solubility of oxygen in water is the dissolved salt content the more salts are dissolved, the less room for oxygen to dissolve. 

If you think about it for a moment, Henry s law makes sense. If we increase the partial pressure of a gas, that means there are more of those gaseous molecules (in a given volume, at a given temperature) zipping around near the surface of the liquid. Doesn t it make sense that more of the gas molecules will be trapped by the liquid solution Also, if the dissolved gas molecules were to escape into the gas phase, the pressure would increase. So, assuming that the pressure remains constant, the would-be escapees are crushed back into solution. 

Partial pressure Pressure due to an individual gas in a mixture of different gases. The partial pressure of a gas equals its mole fraction times the total pressure of the mixture. 

Pressure does not dramatically alter the solubility of solids or liquids, but kinetic molecular theory predicts that increasing the partial pressure of a gas will increase the solubility of the gas in a liquid. If a substance is distributed between gas and solution phases and pressure is exerted, more gas molecules will impact the gas/liquid interface per second, so more will dissolve until a new equilibrium is reached at a higher solubility. Henry s law describes this relationship as a direct proportionality ... 

Equation 8.12 is useful because it allows us to determine the partial pressure of a gas if we know the total pressure and the amount present. The partial pressure of the gas will be proportional to the mole fraction of the gas in the mixture. This can be expressed as Equation 8.13 ... 

Dalton s law of partial pressures When Dalton studied the properties of gases, he found that each gas in a mixture exerts pressure independently of the other gases present. Dalton s law of partial pressures states that the total pressure of a mixture of gases is equal to the sum of the pressures of all the gases in the mixture. The portion of the total pressure contributed by a single gas is called its partial pressure. The partial pressure of a gas depends on the number of moles of gas, the size of the container, and the temperature of the mixture. It does not depend on the identity of the gas. At a given temperature and pressure, the partial pressure of one mole of any gas is the same. Dalton s law of partial pressures can be summarized as... 

The fugacity and partial pressure of a gas are related in the same way as activities and concentrations in solution. Interaction of molecules with each other in a real gas diminishes the reactivity of an individual gas shghtly, creating an effective partial pressure called the godly. As the gas pressure approaches zero, the pressure and fugacity are equal. The interference effect on gases in the atmosphere, however. 

Determination of gas pressures in expired air or blood depends on the application of certain physical principles (Table 27-4). The partial pressure of a gas dissolved in blood is by definition equal to the partial pressure of the gas in an imaginary ideal gas phase in equilibrium with the blood. At equilibrium, the partial pressure (tension) of a gas is the same in erythrocytes and plasma, so that the partial pressure of a gas is the same in whole blood and plasma. The partial pressure of a gas in a gas mixture is defined as the substance fraction of gas (mole fraction) times the total pressure. The tension of a gas in a liquid is, in fact, a measure of the chemical activity of the gas in the liquid. In the physicochemical literature, it is called the fugacity. 

Sj. Mixtures of Real Gases Additive Pressure Law.—The rule that the total pressure of a mixture of gases is equal to the sum of the pressures exerted by each gas if it alone occupied the whole of the available volume ( 5b) does not apply to real gases. The total pressure is thus not equal to the sum of the partial pressures defined in the usual manner. However, for some purposes it is convenient to define the partial pressure of a gas in a mixture by means of equation (5.8), i.e., p == n P, where p is the partial pressure and n is the mole fraction of any constituent of the mixture of gases of total pressure P. 

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