Calculations Comparing Two Reactions

Let s consider the relative effectiveness of two antacids to illustrate how chemical calculations can be important in daily life. Baking soda, NaHC03, is often used as an antacid. It neutralizes excess hydrochloric acid secreted by the stomach. The balanced equation for the reaction is 

Milk of magnesia, which is an aqueous suspension of magnesium hydroxide, Mg(OH)2, is also used as an antacid. The balanced equation for its reaction is 

Which antacid can consume the most stomach acid, 1.00 g of NaHC03 or 1.00 g of Mg(OH)2  

The question we must ask for each antacid is. How many moles of HCl will react with 1.00 g of each antacid  

Two antacid tablets containing HCOj dissolve to produce CO2 gas. 

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Although the FMMF method dramatically reduces the number of substituent constants that one must consider, it suffers from the disadvantage that it is not possible to visually compare two reactions with a three-parameter equation, i.e., one cannot simply plot logs of rates or equilibrium constants against a single parameter as one does in the normal Hammett treatment. It is possible, however, to calculate Hammett substituent constants for any position using the FMMF parameters and the following relationship ... 

DFT calculations for oxidative addition of pentafluorobenzene to Pt(H2PCH2CH2PH2) compared two reaction pathways involving cleavage of the G-F or G-H bond. A hydrido(pentafluorophenyl)platinum complex formed via G-H bond activation and a fluoro(tetrafluorophenyl)platinum complex via G-F bond activation are the kinetic and thermodynamic products, respectively. This tendency contrasts with the reaction of Ni(H2PGH2GH2PH2), which prefers to cleave the G-F bond over the G-H bond. 

The power dissipated at two different frequencies has been calculated for all reactions and compared with the energy loss to the walls. It is shown that at 65 MHz the fraction of power lost to the boundary decreases by a large amount compared to the situation at 13.56 MHz [224]. In contrast, the power dissipated by electron impact collision increases from nearly 47% to more than 71%, of which vibrational excitation increases by a factor of 2, dissociation increases by 45%, and ionization stays approximately the same, in agreement with the product of the ionization probability per electron, the electron density, and the ion flux, as shown before. The vibrational excitation energy thresholds (0.11 and 0.27 eV) are much smaller than the dissociation (8.3 eV) and ionization (13 eV) ones, and the vibrational excitation cross sections are large too. The reaction rate of processes with a low energy threshold therefore increases more than those with a high threshold. 

Knowing the value of the solubility product constant can also allow us to predict whether or not a precipitate will form if we mix two solutions, each containing an ion component of a slightly soluble salt. We calculate the reaction quotient (many times called the ion product), which has the same form as the solubility product constant. We take into consideration the mixing of the volumes of the two solutions, and then compare this reaction quotient to the K.p. If it is greater than the Ksp then precipitation will occur until the ion concentrations reduce to the solubility level. 

Simple collision theory assumes reaction occurs when molecules, with energy greater than a critical minimum, collide. Calculation of two quantities, the total rate of collision of reactant molecules and the fraction of molecules which have at least the critical energy, gives an equation to compare with the experimental Arrhenius... 

The enantiomeric excess of substrate and product shifts during the course of a kinetic resolution, making the determination of the efficiency of the reaction dependent on the reaction time. Hence, two kinetic resolutions can only be compared at the same extent of conversion [45, 62]. For a better comparison of two reactions, equations for the calculation of the enantioselectivity were established [63, 64]. In most cases, the enantiomeric excess of both substrate and product is determined for greater accuracy, but the determination of one and the conversion can also be used for the calculation of the E value (enantioselectivity) ... 

Qualitative NBT ideas provide a straightforward way to think qualitatively about the likely magnitude of the intrinsic barrier for a reaction, or even better for the relative intrinsic barriers of two reactions being compared. If one requires more dimensions, then it will have a larger intrinsic barrier. In general then, the more dimensions there are to a reaction, the larger the intrinsic barrier thus, there is a bias against concerted reactions, but such reactions will be seen when they provide the way to avoid bad intermediates imposed by the stepwise alternatives. Thus, Concerted if necessary but not necessarily concerted. Quantitative NBT provides a convenient, and for most reactions computationally inexpensive, way to calculate rate constants (AG1). Since the predicted rate... 

The activation energies of ozone cycloaddition to the two double bonds of isoprene were found to be comparable (3.3—3.4 kcal mol ) by DFT and ab initio calculations <2002JA2692>. The reaction energies are between —47 and —48 kcal mol-1. 

The same basic formulas for mole conversion with one substance are used to compare two substances in a chemical reaction. The only difference is that one substance must be converted to another using the mole ratio before the calculation can be completed. 

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