Interaction energy-separation curve

We are asked to make a graph that compares the bond properties of F2 and H2. The bond energy is the lowest point on the interaction energy curve, representing the energy minimum for the pair of atoms. Energy in joules is plotted on the y-axis. The bond distance represents optimal separation of the nuclei. 

Fig. 8.8. Interaction energy AW vs adatom separation d for 2H-Cr and 2H-Ti with r] = 1.67. Dashed lines are -Ectdr1 curves. After Schranz (1994).

Schematic forms of the curves of interaction energies (electrostatic repulsion Vr, van der Waals attraction Va, and total (net) interaction Vj) as a function of the distance of surface separation. Summing up repulsive (conventionally considered positive) and attractive energies (considered negative) gives the total energy of interaction. Electrolyte concentration cs is smaller than cj. At very small distances a repulsion between the electronic clouds (Born repulsion) becomes effective. Thus, at the distance of closest approach, a deep potential energy minimum reflecting particle aggregation occurs. A shallow so-called secondary minimum may cause a kind of aggregation that is easily counteracted by stirring.

In Fig. 1.14, the dotted lines for each curve show the activity of the coexisting phases at chemical equilibrium. Similarly in Fig. 1.16 the dotted line BDF shows the activity of the coexisting phases (5 = 0.185 and 0.815). The coexisting phases, which have the same structure, differ in the concentration of vacancies. This phenomenon is generally called phase separation or spinodal decomposition (it is observed not only in the solid phases but also in the liquid phases), and originates from the sign of the interaction energy... 

In this way there is obtained an interaction-energy curve (the lower full curve in Figure 1-7) that shows a pronounced minimum, corresponding to the formation of a stable molecule. The energy of formation of the molecule from separated atoms as calculated by Heitler, London, and Sugiura is about 67 percent of the experimental value of 102.6 kcal/mole, and the calculated equilibrium distance between the nuclei is 0.05 A larger than the observed value 0.74 A. 

FIGURE 11.4 Scaled double-layer interaction energy = K/64nkT)V h) per unit area between two parallel similar plates as a function of scaled separation Kh at the scaled unperturbed surface potential >>o = 1. 2, and 5 calculated with Eq. (11.14) (dotted lines) in comparison with the exact results under constant surface potential (curves 1) and constant surface charge density (curves 2). From Ref. [5]. 

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