C„ dissociation

Figure A3.12.1. Schematic potential energy profiles for tluee types of iinimolecular reactions, (a) Isomerization, (b) Dissociation where there is an energy barrier for reaction in both the forward and reverse directions, (c) Dissociation where the potential energy rises monotonically as for rotational gronnd-state species, so that there is no barrier to the reverse association reaction. (Adapted from [5].)...

Magnesium Hydride. Magnesium hydride is a gray powder of about 97% purity which is insoluble in inert organic solvents. It is easily oxidized, and when heated to about 280°C, dissociates without melting when P is in kPa... 

Common name Formula weight Melting poiut, °C Dissociation constants ia aqueous solution, 25°C AH° at 25°C kj / mol" Solubihty, g/100 g water Reference ... 

Tellurium Tetrabromide. Tellurium tetrabromide [10031-27-3] TeBr, forms yellow hygroscopic crystals which decompose above 280°C and melt at 363°C under bromine vapor. It boils at 414—427°C, dissociating into TeBr2 and bromine. It is soluble in ether and chloroform but not in CCl, and is readily hydroly2ed in water. 

As chlorination proceeds from methyl chloride to carbon tetrachloride, the length of the C—Cl bond is decreased from 0.1786 nm in the former to 0.1755 nm in the latter (3). At ca 400°C, thermal decomposition of carbon tetrachloride occurs very slowly, whereas at 900—1300°C dissociation is extensive, forming perchloroethylene and hexachloroethane and Hberating some chlorine. Subjecting the vapor to an electric arc also forms perchloroethylene and hexachloroethane, as well as hexachlorobenzene, elementary carbon, and chlorine. 

Figure 1.6 Structures and electron density changes of dissociating CO on Ru(OOOl) surface (a) adsorbed CO, (b) transition state for dissociation, and (c) dissociated state.

V4. Vermes, I., Beishuizen, A., Hampsink, R. M and Haanen, C., Dissociation of plasma adreno-corticotropin and cortisol levels in critically ill patients Possible role of endothelin and atrial natriuretic hormone. J. Clin. Endocrinol. Metab. 80, 1238-1242 (1995). 

For a solution of a weak electrolyte of total concentration c, dissociating... 

The form of this equation shows that a graph of log k versus p/L, should be linear with a slope of —n and an intercept of log C. Dissociation of the acid produces the anion hr that accepts protons from water, as shown in the equation... 

Smdies of the thermal degradation of several aromatic acids have been reported. Phthalic acid (80), but not isophthalic acid (81) or terephthalic acid (82), decomposes via dehydration to its anhydride at 140-160 °C. However, (81) and (82) and benzoic acid are thermally stable below 200 °C. Dissociation constants of all 19 isomers of methyl-substimted benzoic acids (83) have been measured in methanol and DMSO. From the pA a values, the substiment effects of the methyl groups were calculated and tentatively divided into polar and steric effects. Also, in the case... 

Formula AICI3 MW 133.31 Structure and bonding an electron-deficient compound, a Lewis acid, occurs as dimer AI2CI6 in hexagonal crystal form. Above 300 °C, dissociation to monomer AICI3 begins completely dissociates to AICI3 at 1,100°C. 

Figure C. Dissociation rates of tris(ethylenediamine)nickel(II) and tris(phenanthroline)nickeI (I I)...

Figure 3.36. Nitrogen dissociation on W(100). (a) Experimental measurements of the dissociation probability S as a function of En and Ts. (b) Experimental measurements of only the direct component of dissociation probability S as a function of Et and 6f. (a) and (b) from Ref. [339]. (c) Dissociation probability S from first principles classical dynamics, separated into a dynamic trapping fraction and a direct dissociation fraction, (d) Approximate reaction path for dynamic trapping mediated dissociation from the first principles dynamics. The numbers indicate the temporal sequence, (c) and (d) from Ref. [343].

Figure 3.44. Dissociation of 02 adsorbed on Pt(lll) by inelastic tunneling of electrons from a STM tip. (a) Schematic ID PES for chemisorbed Of dissociation and illustrating different types of excitations that can lead to dissociation, (b) Schematic picture of inelastic electron tunneling to an adsorbate-induced resonance with density of states pa inducing vibrational excitation (1) competing with non-adiabatic vibrational de-excitation that creates e-h pairs in the substrate (2). (c) Dissociation rate Rd for 0 as a function of tunneling current I at the three tip bias voltages labeled in the figure. Solid lines are fits of Rd a IN to the experiments with N = 0.8, 1.8, and 3.2 for tip biases of 0.4, 0.3, and 0.2 V, respectively and correspond to the three excitation conditions in (a). Dashed lines are results of a theoretical model incorporating the physics in (a) and (b) and a single fit parameter. From Ref. [153].

Physical Properties.—Sulphuryl chloride is a colourless, fuming liquid, with an extremely pungent odour. Z)2 = 1-6074 ->t " = l-4437. It boils at 69-1° C. at 760 mm. pressure, and freezes at —46° C.5 The vapour density is normal at first, but when the chloride is kept, even at 100° C., its vapour commences to dissociate into sulphur dioxide and chlorine. At 200° C. dissociation is almost complete.6 When dissolved in benzene the substance shows a molecular- weight corresponding with S02C12. At ordinary temperatures the specific heat is 0-233, the latent heat of evaporation 32-4 calories per gram, and the heat of formation from the elements approximately 89,540 calories per gram-molecule.7 The dielectric constant at 20° C. is 8-5. As a solvent, the ebullioscopic constant of sulphuryl chloride has been found to have... 

C. Dissociation on Potentials with a Saddle Classical Properties... 

The stable form of nitrogen at room temperature is N2, which has an extraordinarily strong (946 kJ mol-1) triple bond In contrast, white phosphorus consists of P4 molecules (see Chapter 16), and the thermodynamically stable form is black phosphorus, a polymer. At temperatures above 800 °C dissociation to P> molecules does take place, but these are considerably less stable than N2 with a bond energy of488 kJ mol 1. In this case. too. in the heavier element several single bonds arc more effective than the multiple bond. 

In principle, the simplest method for inilialion is to add lo tile purified monomer a small amount of a substance which dissociates to fairly reactive free radicals. This initiator (or sensitizer) is chosen so that its decomposition occurs at a suitable rate at the working temperature thus azoiso-butyronitrile is commonly used at about 60°C dissociating according to the equation ... 

The absolute rate constants were determined for a variety of reactions of the solvated electron in ethanol and methanol. Three categories of reaction were investigated (a) ion-electron combination, (b) electron attachment, and (c) dissociative electron attachment. These bimolecular rate constants (3, 27, 28) are listed in Table III. The rate constants of four of these reactions have also been obtained for the hydrated electron in water. These are also listed in the table so that a comparison may be made for the four rate constants in the solvents ethanol, methanol, and water. 

---