Lewis’ rule

Unfortunately, the ideal-gas assumption can sometimes lead to serious error. While errors in the Lewis rule are often less, that rule has inherent in it the problem of evaluating the fugacity of a fictitious substance since at least one of the condensable components cannot, in general, exist as pure vapor at the temperature and pressure of the mixture. 

Figures 3 and 4 show fugacity coefficients for two binary systems calculated with Equation (10b). Although the pressure is not large, deviations from ideality and from the Lewis rule are not negligible.

The Lewis rules are relatively straightforward easiest to master and the most familiar You will find that your ability to write Lewis formulas increases rapidly with experience Get as much practice as you can early m the course Success m organic chemistry depends on writing correct Lewis structures... 

The limits of the Lewis fugacity rule are not determined by pressure but by composition the Lewis rule becomes exact at any pressure in the limit as y( - 1, and therefore it always provides a good approximation for any component i which is present in excess. However, for a component with small mole fraction in the vapor phase, the Lewis rule can sometimes lead to very large errors (P5, R3, RIO). 

Flo. 3. Vapor-phase solubility of n-decane in nitrogen at 50°C. (a) Ideal gas, (b) virial equation, (c) Lewis rule, (0) experimental. 

Draw all of the structural isomers with the formula C3H6O. Point out any that have geometrical or optical isomers. (Not all structures satisfying Lewis rules correspond to stable chemical substances.)... 

Occupied tetrahedral interstice Couper-Kekule-Van t Hoff-Lewis rules satisfied... 

For many simple compounds having no more than one double bond, the modern picture may be quite adequately represented by the Lewis structures (although the Lewis rules are noncommittal about the shapes of molecules). For compounds such as butadiene, benzene, and nitrous oxide, where there is extensive delocalization of electron density, the Lewis structures are not as suitable as the x-electron structures or, better still, as the streamer structures. Both of the latter type, however, are more difficult to draw and, for more complex molecules, more difficult to visualize they become extremely unwieldy when one attempts to use them to represent the progress of a chemical reaction. 

Lewis has tested this relationship as far as is possible with the data available in the literature, and finds that it is approximately true for all normal unassociated liquids. For associated liquids, such as water, the alcohols and the organic acids, the observed latent heats are considerably greater than those calculated from the coefficient of expansion and the compressibility. This may be due to the additional work necessary to split up the associated molecules. A deviation from Lewis rule may therefore be taken as an indication of the association of the liquid, and is perhaps a better criterion than most of the other methods used for this purpose. The table on p. 153 (taken from Lewis paper) contains the temperature f for which the latent heat was calculated, the calculated and observed latent heats, and, finally, the temperature at which the latent heat was determined. 

When the total molality m is 0.1, significant deviations from Lewis rule are evident. 

Since the ionic strength of solutions 1 and 2 is the same, the chemical potential of Cl" is identical in the two solutions within the approximation of the Lewis rule [Eq. (12-29)]. Consequently, the measured electromotive force in the cell of Eq. (13-124) is identical to the liquid-junction potential. 

Using limiting properties of activity coefficients y in (4.461) (cf. discussion of (4.444)) we find that Lewis rule is valid in the limit of high concentrations Xq, -> 1 at any real fluid mixture. 

Henry s law is traditionally expressed through pressure in (ideal gas) approximation of the type (4.449) with similar approximation the Lewis rule gives Dalton s law (4.424) in the gas phase or Raoult s law in the liquid phase used in vapour-liquid equilibria [152, 154]. 

Similarly, for Lewis-rule ideal solutions, (6.3.2) again reduces to... 

The resulting structure has one more bond than the original and no separation of opposite charges. It is the structural formula for formaldehyde that best satisfies the Lewis rules. 

Applying the Lewis rules to compounds that contain a third-row element such as sulfur is the octet rule. Consider the two stmctural formulas A and B for dimethyl sulfoxide ... 

Lewis rule assumes that (1) the densities of the adsorbates are the same as the densities of the liquid-phase adsorptive and (2) the volumes of the adsorbates add to yield the pore volume. Both assumptions could be incorrect, but for mixing liquid phases, assumption (2) is usually fairly good. These assumptions yield... 

Assuming that Lewis rule applies regardless of the pressure and that the value for j and 2 specified only by the value one expects for the pure adsorbate (1 or 2) at the specified pressure then Eq. (172) could be symbolized as. 

It is clear that within the space of the pores that it is not possible for both adsorbates 1 and 2 to follow the x equation or the standard curve. If adsorbate 1 has a much higher EJ than adsorbate 2 then the adsorption of 1 will predominate and adsorbate 2 will fill out the remaining space according to Lewis rule. Therefore, the value of Xc for adsorbate 1 will remain unchanged, whereas X for adsorbate 2 will change due to the pre-adsorption of 1. For whatever total pressure is used, then Up will equal n i at that pressure. Picking a particular pressure for a standard (in many cases 1 atm at which the experiment is performed) and since n is linear with x, this yields two equations... 

It has been noted in [71] and proved by numerical simulation data that the Lewis rule is not fulfilled in rich H2 + air mixtures. Other cases when Lewis rule is not correct for hydrogenous mixtures have been mentioned in [69]. 

Note that Lewis rules apply to H, C, N, O and F. We willfind that atoms in the next row of the periodic table (e.g., silicon, phosphorus, and sulfur) and beyond commonly violate the octet rule. 

At higher pressures, fugacity can often be calculated by the Lewis rule, which expresses that the fugacity of a gas in a mixture under total pressure P is given by the product of its mole fraction by the fugacity of the same gas at the pure state under the same total pressure hence ... 

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