Change of Gibbs Function

Change in Gibbs function can be derived from the thermod5mamic relations (Equation 3.42c) and expressed as 

Oxygen gas stream is heated from 300 K to 900 K with pressure dropping from 300 kPa to 150 kPa. Calculate the change in enthalpy, change in entropy, and change in Gibbs fimction of the gas stream. 

Enthalpy change based on constant specific heat at an average temperature is given by 

The constant specific heat can be evaluated at an average temperature 

From Table C.4, the function relation for oxygen is given as 

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The change of Gibbs function for polymer solution is expressed with the famous Flory-Huggins equation ... 

This notation is nevertheless widely used, and similarly Seve/ab is often denoted by the symbol AG and called the standard change of Gibbs function or standard (Gibbs) free energy change for the reaction. Equation (6) may then be rewritten in the more usual form ... 

The molar change of Gibbs function on mixing, AuGm, is defined, for a binary mixture containing mole fractions (1 — x) of A and x of B, by the relation ... 

In this section, we will consider the effect of species concentration in reactant and product gas mixtures on the change of Gibbs function reaction and... 

Now, representing the change of Gibbs function in terms of cell voltage given by Equations 4.16 and 4.21, we get... 

Molar specific Gibbs function Gibbs function of formation Change of Gibbs function... 

Stoichiometric factor or fuel utilization factor Thickness of the boundary layer Pressure drop or differential pressure Activation energy for diffusion or barrier energy Change of Gibbs function... 

Arguments have been presented that this difference in changes in Gibbs function, rather than the similar difference in enthalpies of activation, AHl — AH, better represents the quantity with which... 

In the following sections, we introduce the concept of a thermodynamic universe (i.e. a system plus its surroundings). For a reaction to occur spontaneously in a system, we require the change in Gibbs function G to be negative. We then explore the thermodynamic behaviour of G as a function of pressure, temperature and reaction composition. 

Worked Example 4.9 The pressure inside a water pump is the same as the vapour pressure of water (28 mmHg). The pressure of gas inside a flask is the same as atmospheric pressure (760 mmHg). What is the change in Gibbs function per mole of gas that moves Take T = 298 K. 

Or, more conveniently, if G2 is the final value of G and G the initial value of G, then the change in Gibbs function is... 

As chemists, we should perhaps re-cast the question Why is a weak acid weak by asking How does the change in Gibbs function relate to the proportion of reactants that convert during a reaction to form products ... 

H30+. This reaction has an equilibrium constant K of about 2 x 10 5 at room temperature (298 K) when formulated in the usual units of concentration (mol dm 3). What is the associated change in Gibbs function of this reaction ... 

Figure 5.2 Graph of molar Gibbs function Gm as a function of temperature. Inset, at temperatures below r(meit) the phase transition from liquid to solid involves a negative change in Gibbs function, so it is spontaneous...

On opening the drink bottle we hear a hissing sound, which occurs because the pressure of the escaping C02 gas above the liquid is greater than the atmospheric pressure. We saw in Chapter 4 that the molar change in Gibbs function for movement of a gas is given by... 

And the emf of the watch battery is itself a function of the change in Gibbs function, AG(ceu) according to... 

TABLE 8.1. Change in Gibbs Function for Freezing of Supercooled Water... 

Equilibrium Constant and Change in Gibbs Functions and Planck Functions for Reactions of Real Gases... 

As we mentioned, it is necessary to have information about the standard enthalpy change for a reaction as well as the standard entropies of the reactants and products to calculate the change in Gibbs function. At some temperature T, A// j can be obtained from Af/Z of each of the substances involved in the transformation. Data on the standard enthalpies of formation are tabulated in either of two ways. One method is to list Af/Z at some convenient temperature, such as 25°C, or at a series of temperatures. Tables 4.2 through 4.5 contain values of AfZ/ at 298.15 K. Values at temperatures not listed are calculated with the aid of heat capacity equations, whose coefficients are given in Table 4.8. 

Deviations from ideality in real solutions have been discussed in some detail to provide an experimental and theoretical basis for precise calculations of changes in the Gibbs function for transformations involving solutions. We shall continue our discussions of the principles of chemical thermodynamics with a consideration of some typical calculations of changes in Gibbs function in real solutions. 

The value in Equation (20.63) is also the standard change in Gibbs function for the formation of the C4H5O4 ion because, by convention, the corresponding quantity for is set equal to zero [see Equation (20.44)]. 

As in the case of Gibbs function changes, we also can divide the entropy change for a reaction [such as Equation (20.51)] into two parts and can assign one portion to each ion. As actual values of individual-ion entropies cannot be determined, we must establish some convention for apportioning the entropy among the constituent ions. 

In our exposition of the properties of the Gibbs function G (Chapter 7), we examined systems with constraints on them in addition to the ambient pressure. We found that changes in Gibbs function are related to the maximum work obtainable from an isothermal transformation. In particular, for a reversible transformation at constant pressure and temperature [Equation (7.79)],... 

Since in addition to the chemical potentials also the electrical potential 99, affects the charged species, electrochemical potentials //, must be used. We use the symbol 99 instead of -ip because this is the Galvani potential (see Section 5.5). The Gibbs-Duhem equation for changes of state functions at constant temperature is... 

From the relations for general thermodynamic functions, the change of Gibbs energy with pressure is given by... 

This idea can be illustrated in schematic form through the example of the motion of a single curved interface in two dimensions under the action of curvature-induced forces. For convenience, we will represent the interface as a function (rather than via a discrete set of parameters as in the discussion of the variational principle above) of a parameter s as r(x). In this case, the rate of change of Gibbs free energy is given by... 

Another important thing in the synthesis of final products by combustion of metals and nonmetals in nitrogen is the possibility of dissociation of the obtained compounds. The paper [8] was the first to define a change in Gibbs function AG of the system Me-N when determining the direction of the reaction ... 

The change in Gibbs function values can also be determined from the enthalpy of formation and the absolute entropy values. Starting from the definition of Gibbs function asG = H- TS, we can write the change in Gibbs function of the reacting system as follows ... 

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