Chemical equations significance

In liquid metal solutions Z is normally of the order of 10, and so this equation gives values of Ks(a+B) which are close to that predicted by the random solution equation. But if it is assumed that the solute atom, for example oxygen, has a significantly lower co-ordination number of metallic atoms than is found in the bulk of die alloy, dieii Z in the ratio of the activity coefficients of die solutes in the quasi-chemical equation above must be correspondingly decreased to the appropriate value. For example, Jacobs and Alcock (1972) showed that much of the experimental data for oxygen solutions in biiiaty liquid metal alloys could be accounted for by the assumption that die oxygen atom is four co-ordinated in diese solutions. 

In the realm of chemical enumeration we note Polya s equation (4.4) which gives the generating function for stereoisomers of the alkyl radicals, or equivalently, alcohols — that is, equation (5.2) of this article. His equation (4.3) gives the corresponding result for the structural isomers of these compounds. His equations (4.2) and (4.5) correspond, respectively, to the cases of alcohols without any asymmetric carbon atoms and the number of embeddings in the plane of structural formulae for alcohols in general. The latter problem is not chemically very significant. 

These examples suggest that the learner is not always aware which aspects of our use of symbolic representation in chemistiy are intended to be significant. This is an area where further work would be useful, as clearly teachers need to do more to induct learners into the intended symbolism we use in teaching the subject. In the next section, these issues will be explored further in the particular context of learning about chemical equations. 

For the system in problem 1-3, and the equations obtained for part (b), construct an appropriate stoichiometric table. Note the significance of there being more than one chemical equation (in comparison with the situation in problems 2-8 and 2-9). 

The term (2 mol HC1/1 mol H2) is a mole ratio. We got this mole ratio directly from the balanced chemical equation. The balanced chemical equation has a 2 in front of the HC1, thus we have the same number in front of the mol HC1. The balanced chemical equation has an understood 1 in front of the H2, for this reason the same value belongs in front of the mol H2. The values in the mole ratio are exact numbers, and, as such, do not affect the significant figures. 

A balanced chemical equation was used in the calculation. The number of significant digits is correct. The units are also correct. 

Balanced chemical equations provide a significant amount of information. Consider the equation for photosynthesis, the natural process by which green plants form glucose, C6H1206, and oxygen from the reaction of carbon dioxide with water. 

At this point, we should mention the difference between independent chemical equations and independent chemical reactions. The former are of mathematical significance, being helpful to carry out consistent material balance. The latter are useful for describing the chemical steps implied in a chemical-reaction network. They may be identical with the independent stoichiometric equations, or derived by linear combination. This approach is useful in formulating consistent kinetic models. 

Modern theoretical developments in the molecular thermodynamics of liquid-solution behavior are based on the concept of local composition. Within a liquid solution, local compositions, different from the overall mixture composition, are presumed to account for the short-range order and nonrandom molecular orientations that result from differences in molecular size and intermolecular forces. The concept was introduced by G. M. Wilson in 1964 with the publication of a model of solution behavior since known as the Wilson equation. The success of this equation in the correlation of VLE data prompted the development of alternative local-composition models, most notably the NRTL (Non-Random-Two Liquid) equation of Renon and Prausnitz and the UNIQUAC (UNIversal QUAsi-Chemical) equation of Abrams and Prausnitz. A further significant development, based on the UNIQUAC equation, is the UNIFAC method,tt in which activity coefficients are calculated from contributions of the various groups making up the molecules of a solution. 

Chemical Equations. — The mathematical significance of symbols and formulas, together with the conception of the conservation of matter, allows reactions to be represented quantitatively by equations. Chemical equations differ from algebraic equations in one vital respect they are the result of experiment. Thus in Exp. 15 it was shown that magnesium unites with oxygen to form magnesium... 

The given number of moles has three significant figures. Therefore, the answer must have three digits. The balanced chemical equation indicates that 1 mol CjHg produces 3 mol CO2. Thus, 10.0 mol CjHg would produce three times as many moles of CO2, or 30.0 mol. 

The difference between Cp and Cy is of importance only when the volume of the system changes significantly— that is, when different numbers of moles of gases appear on either side of the chemical equation. For reactions involving only liquids and solids, Cp and Cv are for all practical purposes identical. 

A chemical equation of the form A - B represents the transformation of A into B, but it does not imply that all of the reactants will be converted into products, or that the reverse reaction B - A cannot also occur. In general, both processes can be expected to occur, resulting in an equilibrium mixture containing all of the components of the reaction system. (We use the word components when we do not wish to distinguish between reactants and products.) If the equilibrium state is one in which significant quantities of both reactants and products are present (as in the hydrogen iodide example given above), then the reaction is said to incomplete or reversible. 

The chemical equations for reactions that are significantly reversible are written with double arrows as illustrated in Figure 5.5. 

What utility does the equilibrium constant have The reversible arrow in the chemical equation alerts us to the fact that an equilibrium exists. Some measurable quantity of the product and reactant remain. However, there is no indication whether products predominate, reactants predominate, or significant concentrations of both products and reactants are present at equilibrium. 

We will now consider the significance of the term, SMb- Recalling chemical equation (13.7), let us make the dimensionless multiplier, n, numerically equal to the magnitude of SMb -... 

It will have been observed that a certain awkwardness in nomenclature has occurred in the discussion of the reactions. In the formulations of the different reactions, equilibria have been spoken of at times without the intention of conveying the meaning that the various substances taking part existed at definite equilibrium concentrations. The term equilibrium was used in these cases in place of the more usual chemical equation to emphasize the significance of reversibility and mass action effect. 

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