Reduced surface state energy

Very small dispersed particles are highly energetic. In order to approach a stable state, they tend to regroup themselves in order to reduce the surface free energy of the system. An equilibrium will be reached when AG = 0. This condition may be accomplished either by a reduction of the interfacial tension or by a decrease of the total surface area. 

The thermodynamic quantity 0y is a reduced standard-state chemical potential difference and is a function only of T, P, and the choice of standard state. The principal temperature dependence of the liquidus and solidus surfaces is contained in 0 j. The term is the ratio of the deviation from ideal-solution behavior in the liquid phase to that in the solid phase. This term is consistent with the notion that only the difference between the values of the Gibbs energy for the solid and liquid phases determines which equilibrium phases are present. Expressions for the limits of the quaternary phase diagram are easily obtained (e.g., for a ternary AJB C system, y = 1 and xD = 0 for a pseudobinary section, y = 1, xD = 0, and xc = 1/2 and for a binary AC system, x = y = xAC = 1 and xB = xD = 0). 

Tetrahedral N4 is expected to dissociate into two N2 molecules, but this reaction is forbidden by orbital symmetry. Dunn and Morokuma [33] characterized a transition state for the exothermic dissociation of tetrahedral N4 into two N2 and estimated the activation barrier to be 63 kcal/mol at the CASSCF(12e,12o) level, which indicates that N4 is a metastable species with significant kinetic stability. The calculated potential energy surface of N4 suggests that the low-lying triplet state might cross with the singlet surface (Fig. 3), which could reduce the activation energy barrier to about 30 kcal/mol [29,31,32],... 

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