PE-pC diagrams

The pe-pC diagram conveys the idea that both Fe and Fe + have regions where they can be the predominant species in water at pH 2. However, if Fe + is to predominate and be in equilibrium with the Oa/HgO couple, the solution must essentially be stripped of dissolved oxygen. For example, at pe values of less than 13, Fe will predominate whep the oxygen partial pressure in equilibrium with the water couple is less than 10-22... 

In this section we will first present the development of a simple diagram (the so-called pe-pC or E -pC diagram) for a reaction that involves only electron transfer in a homogeneous system. Next we will consider the predominance area diagrams for presenting combined redox and acid-base equilibria. Finally, we will add a third dimension and consider systems with multiple phases using the pe-pH predominance area diagram. 

Figure 17. Composition diagram of expected specific impulse for ammonium perchlorate-aluminum-polyurethane (PU) propellant (polyester binder). Pc/Pe = 1000/14.7 p.s.i.a. 10KS-2500 motors...

The thermodynamic process can be indicated both on a P-V (pressure-volume) diagram and on a h-S(enthalpy-entropy) diagram as shown in figure n. A. 2. The propellants enter the chamber at point i and are gasified. They react as a constant pressure, pc, and then they are expanded isentropically through the nozzle to the exhaust pressure pe. The throat conditions are noted with the subscript t. 

We proceed with the construction of this diagram using methods similar to those employed for preparing acid-base equilibrium diagrams. Although we use pe in our development of the diagram (Fig. 7-3), we can show EH versus pC too, since pe has a fixed relationship to E, for example, at 25 C, pe= 16.9E (Eq. 7-19). 

After plotting these points, we can complete the diagram in the vicinity of pe = pe° as shown. The straight line portions of each line are connected with the curved lines in the region approximately one pe unit from pe", just as was done for the pC-pH diagrams for acid base systems. However, this latter step depends on the slopes of the concentration lines. 

Figure 6.1 Schematic cross-section through monolayer of amphiphilic molecules consisting of polar head (solid dot) and hydrocarbon chain. (PCs, PEs and DGDGs are two-chain molecules with zwitterionic polar heads.) The thickness of the monolayer h, as well as the positions of the neutral surface z , and the actual bending surface, Z, are indicated in the flat state for co < 0 (see text). The sign of curvature is defined by the lower diagram.

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