Gas mixtures partial pressures

For an ideal gas mixture, partial pressure is directly proportional to mole fraction thus, we can write the following ... 

Other composition variables are sometimes used, such as volume fraction, mole ratio, and mole percent. To describe the composition of a gas mixture, partial pressures can be used (Sec. 9.3.1). 

The total pressure can be regarded as a sum of the parts furnished by the individual pressures exerted by each of the components of the gas mixtures. The pressure exerted by each of the gases in a gas mixture is called the partial pressure of that gas. The partial pressure is the pressure that the gas would exert if it were alone in the container. In the example of Figure 4-3, the total pressure in the third bulb is 113 mm. The partial pressure of water vapor in this bulb is 20 mm and the partial pressure of air is 93 mm. 

The pressure of a gas is due to the impacts of the molecules on the walls of the container. The greater the number of molecules, the higher the pressure. In a gas mixture, the pressure that each gas would exert if it occupied the same volume by itself at the same temperature is called the partial press are. The ideal gas law, Equation l 1-3, can t distinguish between gases it works equally well for a pure gas or a gas mixture. For a given temperature and volume the pressure of a single gas (A) is given by... 

We next consider the dissolution of a mixture of gases in a liquid. We separate this situation into two different cases. First, if the concentrations of the dissolved gases in the liquid are relatively low, so that there are no nonideality departures from Henry s law, it is reasonable to assume that the solubility of each gas would be the same as if it were the only gas present at its gas-phase partial pressure. However, if the concentrations of the gases in the liquid are high enough that there are departures from the Henry s law limit, so that the activity coefficients yT need be included in the description, then the solubility of each species is affected by the presence of others through the values of the activity coefficients. 

Adsorption. Adsorption occurs when a fluid mixture comes into contact with a solid surface. Purification of a gas or liquid by adsorption of impurities on charcoal is a typical example. Adsorption mechanisms can be quite complex, but equilibrium can be represented by isotherms showing the amount of a given component adsorbed by a unit of solid adsorbent, which is a fimction of gas-phase partial pressure or liquid-phase concentration. 

Rearrangements of the ideal gas law are used to calculate the rtvrlar mass of a gas, the density of a gas, the partial pressure of each gas in a mixture of gases, and the amounts of gaseous reactants or products in a reaction. 

The total absolute pressure, P, exerted by a mixture of N ideal gases is the sum of the partial pressures, of each gas. The partial pressure, is the pressure of a gas it would exert if it occupied the container alone. 

The pressure exerted by a particular gas in a mixture is the partial pressure of that gas. The partial pressure of hehum in the preceding mixture is 152 mmHg the partial pressure of hydrogen in the mixture is 608 mmHg. According to Dalton s law of partial pressures, the sum of the partial pressures of all the different gases in a mixture is equal to the total pressure of the mixture. 

Partial pressure of the component i in a mixture Partial pressure of the component i at the inlet of gas channel Critical pressure Power per cell... 

For a pure gas the partial pressure is equal to the total pressure (because y, = 1.0 for a pure gas). For any gas mixture the sum of the partial pressures equals the total pressure, = PJlyi = P because the sum of the mol fractions is unity. The partial pressure is defined only for gases this term is not used for solids and liquids. 

When the vapor phase mixture behaves as a perfect gas, the partial pressure of the /th component is governed by Dalton s law as given by... 

In a gas mixture, the pressure that each gas exerts as part of the total pressure is called the partial pressure of that gas. Because the air sample is a mixture of gases, the total pressure is the sum of the partial pressures of each gas in the sample. 

At pressures to a few bars, the vapor phase is at a relatively low density, i.e., on the average, the molecules interact with one another less strongly than do the molecules in the much denser liquid phase. It is therefore a common simplification to assume that all the nonideality in vapor-liquid systems exist in the liquid phase and that the vapor phase can be treated as an ideal gas. This leads to the simple result that the fugacity of component i is given by its partial pressure, i.e. the product of y, the mole fraction of i in the vapor, and P, the total pressure. A somewhat less restrictive simplification is the Lewis fugacity rule which sets the fugacity of i in the vapor mixture proportional to its mole fraction in the vapor phase the constant of proportionality is the fugacity of pure i vapor at the temperature and pressure of the mixture. These simplifications are attractive because they make the calculation of vapor-liquid equilibria much easier the K factors = i i ... 

According to Dalton s laM of partial pressures, observed experimentally at sufficiently low pressures, the pressure of a gas mixture m a given volume V is the sum of the pressures that each gas would exert alone in the same volume at the same temperature. Expressed in tenns of moles n. 

The partial pressure p- of a component in an ideal-gas mixture is thus... 

Given this experimental result, it is plausible to assume (and is easily shown by statistical mechanics) that the chemical potential of a substance with partial pressure p. in an ideal-gas mixture is equal to that in the one-component ideal gas at pressure p = p. 

Experiments on sufficiently dilute solutions of non-electrolytes yield Henry s laM>, that the vapour pressure of a volatile solute, i.e. its partial pressure in a gas mixture in equilibrium with the solution, is directly proportional to its concentration, expressed in any units (molar concentrations, molality, mole fraction, weight fraction, etc.) because in sufficiently dilute solution these are all proportional to each other. 

When Che diameter of the Cube is small compared with molecular mean free path lengths in che gas mixture at Che pressure and temperature of interest, molecule-wall collisions are much more frequent Chan molecule-molecule collisions, and the partial pressure gradient of each species is entirely determined by momentum transfer to Che wall by mechanism (i). As shown by Knudsen [3] it is not difficult to estimate the rate of momentum transfer in this case, and hence deduce the flux relations. 

The composition of the vapour can easily be calculated as follows — Assuming that the gas laws are applicable, it follows that the number of molecules of each component in the vapour wdll be proportional to its partial pressure, i.e., to the vapour pressure of the pure liquid at that temperature. If and p are the vapour pressures of the two liquids A and B at the boiling point of the mixture, then the total pressure P is given by ... 

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