Gibbs energy variation with pressure

Variation of Gibbs Energy, G With Pressure, P at Constant Temperature (dT = 0) and Variation of Entropy, S With Pressure, P at Constant Temperature (dT = 0) for an Idea Gas... 

Variation of Gibbs Energy, G with Pressure, P at Constant Temperature (dT = 0)... 

Thermodynamics is used to predict whether reactants have a spontaneous tendency to change into products. This tendency is associated with a decrease in the free energy or Gibbs energy of the system (G) to a minimum. As a consequence, the thermodynamic criterion for spontaneous change at constant temperature and pressure is AG < 0. Under standard conditions (concentrations = 1 M, and P = 1 atm), the standard Gibbs energy variation (AG°) is related with the equilibrium constant (A) by equation 11 ... 

FIGURE 8.4 The variation of the molar Gibbs free energy of an ideal gas with pressure. The Gibbs free energy has its standard value when the pressure of the gas is 1 bar. The value of the Gibbs free energy approaches minus infinity as the pressure falls to zero. 

The variation in Gibbs-free-energy change with temperature at constant pressure is given by... 

Example 2.4. Thermodyanmics of COi Dissolution in Water Describe the variations in the entropy, enthalpy, and Gibbs energy with extent of CO2 dissolution for a two-phase system comprising a gas phase and an aqueous phase. Find the equilibrium state. Initially, a liter of gas at 1 atm total pressure contains 2 X 10 mol of CO2. It is brought into contact with a liter of pure water. The dissolution process is... 

The fugacity concept was introduced initially to account for the non-ideal behaviour of real gases. Later the concept was generalised to phase equilibrium calculation. Let us go back to the equation describing the variation of Gibbs energy with the pressure at... 

It is important to realize that however valuable PVT information is (and it is extremely valuable in the chemical industries), it is not thermodynamically complete information. You cannot calculate a heat capacity from PVT data, and this means that you cannot calculate the temperature variation of the Gibbs energy, enthalpy, or entropy. You can calculate the pressure variation of these functions, but you need to start with a baseline showing the variation with T at some pressure. There is a second important class of EoS, sometimes called thermal EoS, which do provide complete information, and these are equations based on G T, P) or A T, V). We will look first at PVT equations of state. 

The shape of the curve representing the variation of AG with a is qualitatively shown in Figure 6.9, for p(R = a)> p(R = o). The function AG(fl) contains a maximum at a certain value for a, the so-called critical radius a. Because, at constant p and T, any spontaneous process is characterized by a decrease in the Gibbs energy, introducing a liquid droplet of radius a into a vapor of pressure p leads to further growth of the droplet ifa>a but if a < a, the droplet vaporizes. 

The ELBT program on the CD-ROM permits the correlation of isothermal VLE data of homogeneous binary systems with equations derived from the Redlich-Kister expansion. Vapor-phase imperfection and the variation of the Gibbs energy of the pure liquid components are accounted for through the second molar virial coefficients By and the molar volumes V° under saturation pressures (Chap. 3.5.5). The correlated total vapor pressure P and... 

Knowing the state equation or the variations in the compressibility coefficient Z with pressure, we can then calculate the integral of the second member and therefore molar Gibbs energy of the real gas. However, this method does not allow us to calculate the term g (T) which proves the inability of a state equation to completely define a gas. 

The variation of Gibbs energy with pressure The variation of Gibbs energy with temperature... 

Variation of the Gibbs energy with pressure (for an incompressible liquid). 

Fig, 3.1 The variation of molar Gibbs energy with pressure. The region of stability of each phase is indicated in the band at the bottom of the illustration. 

Fig. 3.2 The variation of the molar Gibbs energy of a perfect gas with pressure.

Fl 3.31 The variation of the Gibbs energy of dissolving with composition for two components at constant temperature and pressure. Note that AG < 0 for all compositions, which indicates that two components mix spontaneously in aU proportions. 

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