Mixtures of ideal gases

The heart of the question of non-ideality deals with the determination of the distribution of the respective system components between the liquid and gaseous phases. The concepts of fugacity and activity are fundamental to the interpretation of the non-ideal systems. For a pure ideal gas the fugacity is equal to the pressure, and for a component, i, in a mixture of ideal gases it is equal to its partial pressure yjP, where P is the system pressure. As the system pressure approaches zero, the fugacity approaches ideal. For many systems the deviations from unity are minor at system pressures less than 25 psig. 

This states that the total pressure of a mixture of ideal gases is equal to the sum of the partial pressures of the constituent gases. The partial pressure is defined as the pressure each gas would exert if it alone occupied the volume of the mixture at the mixture s temperature. 

The fugacity coefficient is a function of pressure, temperature, and gas composition. It has the useful property that for a mixture of ideal gases (Pi = 1 for all i. The fugacity coefficient is related to the volumetric properties of the gas mixture by either of the exact relations (B3, P5, R6) ... 

The total pressure in the container is the sum of the partial pressures Aotal He + PO2 We have used He and O2 to illustrate the behavior of a mixture of ideal gases, but the same result is obtained regardless of the number and identity of the gases. 

Consider an ideal mixture of ideal gases, A and B. Equation 9 yields... 

The simplest solution one can imagine is a mixture of ideal gases. Let us simplify the case by assuming only two types of ideal gas molecules, A and B, in the mixture. The total pressure in this case is the sum of the partial pressures of the two components (this is termed Dalton s law). Thus,... 

The thermodynamic development above has been strictly limited to the case of ideal gases and mixtures of ideal gases. As pressure increases, corrections for vapor nonideality become increasingly important. They cannot be neglected at elevated pressures (particularly in the critical region). Similar corrections are necessary in the condensed phase for solutions which show marked departures from Raoult s or Henry s laws which are the common ideal reference solutions of choice. For nonideal solutions, in both gas and condensed phases, there is no longer any direct... 

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. 

We will see that the relationships that are derived for mixtures of ideal gases will form convenient bases for the treatment of nonideal gases and solutions. 

For the reaction [Equation (9.47) applied to a mixture of ideal gases]... 

MIXTURES OF GASES AND EQUILIBRIUM IN GASEOUS MIXTURES mixture of ideal gases. Thus,... 

Equation (14.2) clearly reduces to the historical form of Raoult s law [Equation (14.1)] when the vapors are an ideal mixture of ideal gases. 

The equilibrium constant defined by eqn. (26) can be used to calculate the equilibrium conversion of reactants to products under specified conditions of temperature and pressure. The activity of a component X in a mixture of ideal gases, Ox, is given by... 

The basic expressions for the mass fluxes and the equations of continuity for multi-component mixtures are given in Sec. II,B. For a -component mixture of ideal gases in a system in which there is no pressure diffusion, forced diffusion, or thermal diffusion, the fluxes are given by... 

Fet us now consider a c-component mixture of ideal gases. In this case, Dalton s law of partial pressures tells us that each gas exerts a partial pressure Pt proportional to its... 

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. 

Remember that this is valid only for ideal mixtures of ideal gases. 

EXAMPLE 3-3 Calculate the partial pressure exerted by methane in the following gas when the gas is at a pressure of 750 psia. Assume that the gas is a mixture of ideal gases. 

Boyle s Equation —Charles Equation—Avogadro s Law — The Equation of State for an Ideal Gas — Density of an Ideal Gas — Kinetic Theory of Gases Mixtures of Ideal Gases 100... 

The mole fraction of a component of a mixture is the number of moles of the component divided by the sum of the number of moles of all the components of the mixture. As a mole of every ideal gas occupies the same volume, it follows by Avogadro s law that in a mixture of ideal gases the mole fraction of a component will exactly equal the volume fraction ... 

---