Ideal mixture of real gases

Two further crude approximations have been used for the virial equation of state. The first is that the virial coefficients combine linearly. This combination of constants results in an equation of state that is additive in the properties of the pure components. In such a mixture Dalton s and Amagat s laws still hold, and the mixture may be called an ideal mixture of real gases. The assumption is probably the crudest that can be used and is... 

For an ideal mixture of real gases (/ = yJi) we have cpi = 9 . There hold the relation... 

The fugacity coefficient of the i-th constituent in an ideal mixture of real gases can be calculated as follows ... 

In mixtures of real gases the ideal gas law does not hold. The chemical potential of A of a mixture of real gases is defined in terms of the fugacity of the gas, fA. The fugacity is, as discussed in Chapter 2, the thermodynamic term used to relate the chemical potential of the real gas to that of the (hypothetical) standard state of the gas at 1 bar where the gas is ideal ... 

In this chapter we will apply the concepts developed in Chapter 11 to gaseous systems, first to mixtures of ideal gases, then to pure real gases, and finally to mixtures of real gases. 

Since the petroleum engineer primarily is concerned with gas mixtures, the laws governing the behavior of mixtures of ideal gases will now be introduced. This will later lead to an understanding of the behavior of mixtures of real gases. 

The rationalizations of signs for HE of binary liquid mixtures presented in Sec. 16.7 apply approximately to the signs of S 2 for binary gas mixtures. Thus, positive Su is the norm for NP/NP, NA/NP, and AS/NP mixtures, whereas is usually negative for NA/NA mixtures comprising solvating species. One expects < 12 to be essentially zero for ideal solutions of real gases, e.g., for binary gas mixtures of the isomeric xylenes. 

What has been discussed is valid if it is assumed that a mixture of real gases is ideal ... 

The definition of tlie fugacity of a species in solution is parallel to the definition of tire pure-speciesfugacity. For species i m a mixture of real gases or in a solution of liquids, the equation analogous to Eq. (11.28), tire ideal-gas expression, is ... 

A simple modification of the law of partial pressures as applied to ideal gases has been proposed for mixtures of real gases (E. P. Bartlett, 1928). If PJ is the pressure which would be exerted by a constituent of a gas mixture when its molar volume is the same as that of the mixture, then it is suggested that the total pressure P is given by... 

Gas mixtures Ideal perfect mixture, p= bar. Mixture of real gases,yj=l bar. 

But, following the discussion given at the end of iii. above and similarly as for the first pure interpretation of (4.417), we can interpret (4.422) as a limiting property of each real gas mixture of fixed composition, i.e. property (A.3) is valid also for mixtures of real gases which therefore in the limit of zero pressures behaves as an ideal gas mixture with state equation (4.421). 

Operations of most fuel cell power systems involve a mixture of gases. Therefore, we need to perform thermodynamic analysis and transport phenomena analysis with a mixture of gases. The gas mixture may be a mixture of ideal gases or a mixture of real gases. In this book, the presentation of fuel cell analysis is restricted to the mixture of ideal gases only. 

This is why an ideal solution of gases is also referred to as an "ideal solution or mixture of real gases". Thus an ideal gas is an ideal solution, but the reverse is not necessarily the case. 

Determine the equilibrium conversion for the production of methanol from a stoichiometric ratio of CO and H2 at 275°C and 1(X) atm. Assume the mixture to be an ideal one of real gases. 

Equations 9.3-3 to 9.3-5 resemble those obtained in Sec. 9.1 for the ideal gas mixture. There is an important difference, however. In the present case we are considering an ideal mixture of fluids that are not ideal gases, so each of the pure-component properties here will not be an ideal gas property, but rather a real fluid property that must either be measured or computed using the techniques described in Chapter 6. Thus, the molar volume Vj is not equal to RT/P, and the fugacity of each species is not equal to the pressure. 

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