Benson

However, such a level can still be considered too high for vehicles having 3-way catalytic converters. In fact, results observed in the United States (Benson et al., 1991) and given in Figure 5.20 show that exhaust pollutant emissions, carbon monoxide, hydrocarbons and nitrogen oxides, increase from 10 to 15% when the sulfur level passes from 50 ppm to about 450 ppm. This is explained by an inhibiting action of sulfur on the catalyst though... 

Benson, J.D. et al. (1991), Effects of gasoline sulfur level on mass exhaust emissions . SAE paper No. 91-2323, International fuels and lubricants meeting, Toronto, Ontario. 

It is important to evaluate the surface distortion associated with the assymetric field at the surface, a difficult task often simplified by assuming that distortion is limited to the direction normal to the plane [64, 6S]. Benson and co-workers [6S] calculated displacements for the first five planes in the (100) face of sodium chloride and found the distortion correction to of about 100 ergs/cm or about half of itself The displacements show a tendency toward ion pair formation, suggesting that lateral displacements to produce ion doublets should be considered [66] however, other calculations yielded much smaller displacements [67]. 

An excellent example of work of this type is given by the investigations of Benson and co-workers [127, 128]. They found, for example, a value of = 276 ergs/cm for sodium chloride. Accurate calorimetry is required since there is only a few calories per mole difference between the heats of solution of coarse and finely divided material. The surface area of the latter may be determined by means of the BET gas adsorption method (see Section XVII-5). 

Rate effects may not be chemical kinetic ones. Benson and co-worker [84], in a study of the rate of adsorption of water on lyophilized proteins, comment that the empirical rates of adsorption were very markedly complicated by the fact that the samples were appreciably heated by the heat evolved on adsorption. In fact, it appeared that the actual adsorption rates were very fast and that the time dependence of the adsorbate pressure above the adsorbent was simply due to the time variation of the temperature of the sample as it cooled after the initial heating when adsorbate was first introduced. 

Golden D M and Benson S W 1975 Physicai Chemistry. An Advanced Treatise vol VII (New York Academic) p 57... 

In fact, there is a hierarchy in calculating molecular properties by additivity of atomic, bond, or group properties, as was pointed out some time ago by Benson [1, 2]. The larger the substructures that have to be considered, the larger the number of inaements that can be derived and the higher the accuracy in the values obtained for a molecular property. 

Figure 7-1 shows the groups that are obtained for alkanes, and the corresponding notation of these groups as introduced by Benson [Ij. Table 7-2 contains the group contributions to important thermochemical properties of alkanes. Results obtained with these increments and more extensive tables can be obtained from Refs. [1] and [2]. 

Figure 7-1. The four groups contained in alkanes, and their linear code as introduced by Benson [1].

In order to develop a quantitative interpretation of the effects contributing to heats of atomization, we will introduce other schemes that have been advocated for estimating heats of formation and heats of atomization. We will discuss two schemes and illustrate them with the example of alkanes. Laidler [11] modified a bond additivity scheme by using different bond contributions for C-H bonds, depending on whether hydrogen is bonded to a primary (F(C-H)p), secondary ( (C-H)g), or tertiary ( (C-H)t) carbon atom. Thus, in effect, Laidler also used four different kinds of structure elements to estimate heats of formation of alkanes, in agreement with the four different groups used by Benson. 

All three schemes, the Benson, the Laidler, and the Allen scheme, use four structure contributions for the estimation of thermochemical data of alkanes. As might be guessed, they are numerically equivalent all three schemes provide the same accuracy. This is shown below by Eqs. (7)-(10) for the interconversion of the various contributions. 

S.W Benson, Thermochemical Kinetics, 2nd edition, Wiley, New York, 1976. 

The b vector in this equation set has been converted from kilocalories per mole (Benson and Cohen, 1998) to kilojoules per mol. Solve these simultaneous equations to obtain the energetic conPibutions for P, S, T, and Q. 

Our results are in very good agreement with Benson s simpler bond additivity values (2.5 kcal mol and —3.75 kcal mol Benson and Cohen, 1998), as indeed they must be because they were obtained from the same set of experimental enthalpies of formation. Note that many applications in themiochemishy use energy units of kilocalories per mole, where 1.000 kcal mol =4.184 kJ mol . ... 

Benson, S. W. Cohen, N., 1998. In Computational Thermochemistty, Irikura, K. K. Frurip, D. J. eds., ACS Symposium Series 677 American Chemical Society, Washington, DC. 

In the fall of 1976 I had a call from a friend, Sid Benson, who, after a decade at the Stanford Research Institute, just returned to the University of Southern California (USC) in Los Angeles. He invited me for a visit, telling me about USC s plans to build up seleeted programs, ineluding chemistry. I visited USC and found it, with its close to downtown urban campus, quite different from the sprawling expanse of the eross-town eampus of UCLA, whieh I had visited on a number of oe-... 

Physical facilities help, but do not per se make a research institute. It is the people who work there and their contributions and devoted hard work that is most important. We are nearing a quarter of a century since the Hydrocarbon Research Institute was started at USC. At the beginning in 1977, Sid Benson and I shared the scientific directorship of the Institute and Jerry Segal carried out the administrative responsibilities as executive director. When we moved into our own building in 1979, Bill Stephenson, a physical-organic chemist and a former colleague of mine in Cleveland who subsequently joined us at... 

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