Hess rule

According to Berman and Newman [ 156] the C3A hydration with ettringite formation is accompanied by the heat evolution on the level 816 J/g SO3 with the monosulphate formation—783 J/g respectively. Applying the Hess rule one can write ... 

The heat of hardening can be determined not only by a simplified ealculation, but by direct calorimetric measurements, or indirectly applying the Hess rule. According to this rule, the heat of reaction depends only on the initial and final state and this is the basis of the dissolution method. In this dissolution procedure, the heat of hardening is determined as a difference between the heat of neat cement dissolution and heat of hydration products (cement paste) dissolution. The mixture of nitric and fluoric acids is used for this purpose. Only the dissolution method is applied in the case of the longer hydration time. The most accurate, differential calorimetric method has been developed by Zielenkiewicz [164]. The completely hydrated mortar is placed in one container of calorimeter and in the second one— the fiesh mortar. 

During the next three decades there was a continual growth in the use and number of color additives, and using Hesse s rules, the Hst of colors certifiable for use in foods was expanded. 

Section 6.11, when we calculated the enthalpy change for an overall physical process as the sum of the enthalpy changes for a series of two individual steps. The same rule applied to chemical reactions is known as Hess s law the overall reaction enthalpy is the sum of the reaction enthalpies of the steps into which the reaction can be divided. Hess s law applies even if the intermediate reactions or the overall reaction cannot actually be carried out. Provided that the equation for each step balances and the individual equations add up to the equation for the reaction of interest, a reaction enthalpy can be calculated from any convenient sequence of reactions (Fig. 6.30). 

With Dunlap casting the deciding vote, the Board ruled in November that, under the law, other dyes could not and should not be forbidden unless the Bureau of Chemistry (i.e. Hesse) could present evidence that the dyes in question were harmful to human health. Considering the number of dyes on the market, this was tantamount to rejecting mandatory certification. Still, the decision reached was inescapable to one concerned, as McCabe was, with the text of the law as enacted. The statute only expressly prohibited poisonous color in confectionary, and under the general adulteration clause, prohibited any added ingredient which would render a food harmful to health. This was as far as McCabe would go. The question of moral propriety was simply not relevant. It was the duty of the executive branch to enforce the law ns enacted, and not to legislate (59) ... 

By applying the Hess additivity rule to the involved energy terms, we have ... 

If a process can be imagined to occur in successive steps, AH for the overall process is equal to the sum of the enthalpy changes for the individual steps. This rule, sometimes called Hess s law of constant heat summation, has many applications in thermochemistry. 

Verkuyten, M., Rood-Pijpers, E., Elffers, H. and Hessing, D. (1994) Rules for breaking formal rules Social representations and everyday rule-governed behaviour. The Journal of Psychology 128 (5), 485—498. 

The following Rule of Lavoisier and Laplace is really a corollary of the Hess s Law. 

This problem requires more effort. The two rules of Hess s Law must be applied ... 

In fact, the enthalpy change of any reaction can be determined in the same way—the reactants can be converted to their elements, and the elements can be recombined into the products. Why Hess s law states that the overall enthalpy change of a reaction is the same, whether for a single-step process or a multiple step one. If you apply this rule, the exothermic reaction that forms sulfur trioxide and nitrogen oxide has the enthalpy change listed below. 

Entropies can also be calculated by using Hess s law and entropy data for other reactions. This statement means that you can manipulate chemical equations using rules of algebra to get a desired equation. But remember that when equations are added or subtracted, entropy changes must be added or subtracted. And when equations are multiplied by a constant, the entropy changes must also be multiplied by that constant. Finally, atoms and molecules that appear on both sides of the equation can be canceled. 

Carter, D.E., Hess, B.W., Scholljegerdes, E.J., and Rule, D.C. 2002. Effect of supplemental soybean oil on duodenal flow of long chain fatty acids in beef heifers grazing summer pasture. Proc.. Western Sect., Am. Soc. Anim. Sci. 53, 646-650. 

Hess law, 30, 85, J46 heteropolar bond, 23 heteropolymetallate, 223 high-spin complex, 213 HOMO, 75, 90 homopolar bond, 23 H ckel theory, 82 Hund s first rule, KL, 11, 70 hybridization, 73, 77 hydrazine, 162 hydride, 26,129,150 hydroformylation, 268 hydrogen bond, 79, 91, 151 hydrogen electrode, 140, 143 hydrogen peroxide, 171, 266 hydrogenation, 268 hydrothermal reaction, 41, 114, 257 hydroxide, 130,132,138,119,110 hypervalence, see octet expansion... 

The change in state of a system produced by a specified chemical reaction is definite. The corresponding enthalpy change is definite, since the enthalpy is a function of the state. Thus, if we transform a specified set of reactants to a specified set of products by more than one sequence of reactions, the total enthalpy change must be the same for every sequence. This rule, which is a consequence of the first law of thermodynamics, was originally known as Hess s law of constant heat summation. Suppose that we compare two different methods of synthesizing sodium chloride from sodium and chlorine. 

The propagation of concentric and spiral waves of Ca in Xenopus oocytes has also been studied (Lechleiter et al., 1991) by means of simulations based on cellular automata (Gerhard, Schuster Tyson, 1990 Markus Hess, 1990) such a mathematical representation of excitable systems in terms of a set of rules simulated on a computer considers the existence of a finite number of cell states (excitable, excited, refractory). The comparison of numerical simulations with experiments suggested (Lechleiter et al, 1991) that the species responsible for the spatial propagation of the wave is cytosolic rather than IP3. Moreover, the characteristics of the phenomenon fit with the view (Berridge Irvine, 1989) that CICR is the primary mechanism imderlying Ca " wave propagation. 

From the rule known as Hess s law, which is simply a special case of the conservation of energy,... 

Bolte, M. R., Hess, B. W., Means, W. J., Moss, G. E., Rule, D. C. (2002). Feeding lambs high-oleate or high-linoleate safflower seeds differentially influences carcass fatty acid composition. Journal of Animal Science, 80, 609-616. 

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