Chemical equation information

F i ure 4.5 A combustion reaction. Here propane burns in air to give carbon dioxide and water. The balanced chemical equation informs us that one molecule of propane will combine with five molecules of oxygen to give three molecules of carbon dioxide and four molecules of water. Photo, C. D. Winters model, S. M. Young)... 

The essential information implied by the chemical equation is the stoichiometry at the macroscopic level, ie, if a moles of M react, then b moles of B do also p moles of P are formed, etc. No inference should be made about behavior at the microscopic or atomic level, ie, there is no implication thatp molecules of P appear simultaneously. There may or may not be intermediates that appear and disappear in the course of the reaction. 

Mechanisms. Mechanism is a technical term, referring to a detailed, microscopic description of a chemical transformation. Although it falls far short of a complete dynamical description of a reaction at the atomic level, a mechanism has been the most information available. In particular, a mechanism for a reaction is sufficient to predict the macroscopic rate law of the reaction. This deductive process is vaUd only in one direction, ie, an unlimited number of mechanisms are consistent with any measured rate law. A successful kinetic study, therefore, postulates a mechanism, derives the rate law, and demonstrates that the rate law is sufficient to explain experimental data over some range of conditions. New data may be discovered later that prove inconsistent with the assumed rate law and require that a new mechanism be postulated. Mechanisms state, in particular, what molecules actually react in an elementary step and what products these produce. An overall chemical equation may involve a variety of intermediates, and the mechanism specifies those intermediates. For the overall equation... 

Write, balance, and label a chemical equation on the basis of information given in sentence form (Example H.l). 

Some tasks in the Test of Gained Knowledge required students to connect observations about the macro course of chemical reactions with their notations in the submicro and/or symbolic types of representation. The results indicate that most students were able to rearticulate the information about reactants and products of a chemical reaction from the textual description of chemical reaction into the form of word chemical equation (textual description of macros word equation of macro Task 8.2, f(o/ )=89.82% Task 9.1, f(o/ )=87.61%). This action corresponds to the first step in learning to write down chemical equation in the LON approach. It can easily be explained, because teachers described the learning process to be very efficient to this point, as is illustrated below ... 

The style of the book is to present only a small amount of information on each page with a slide-like illustration using short descriptions and easily understood chemical equations and structures. Under each illustration is additional information or comments with room for the reader to make notes if desired. Although there is obvious continuity, an attempt has been made to make each page subject somewhat independent so that readers can study the contents of the book one page at a time at their own pace. Of necessity, because of this format, there is considerable repetition. We do not consider this bad. 

The net ionic equation, like all balanced chemical equations, gives the ratio of moles of each substance to moles of each of the others. It does not immediately yield information about the mass of the entire salt, however. (One cannot weigh out only Ba2+ ions.) Therefore, when masses of reactants are required, the specific compound used must be included in the calculation. The use of net ionic equations in stoichiometric calculations will be more important after study of molarity (Chap. 10). 

The information for the calculation is organized around the chemical equation. Let x = mol H2 (or I2) that reacts. Then use stoichiometry to determine the amount of HI formed, in terms of x, and finally solve for x. 

We use the balanced chemical equation as a basis to organize the information we have about the reaction. 

We organize this information around the balanced chemical equation, as before. We recognize that as much hydronium ion (a strong acid) as possible will react to produce the weak acid, acetic acid. 

A proper set of chemical equations provides an aid in chemical book-keeping to determine composition as reaction proceeds. This is the role of chemical stoichiometry. On the one hand, it prescribes elemental balances that must be obeyed as constraints on reaction on the other hand, in prescribing these constraints, it reduces the amount of other information required (e g., from kinetics) to determine the composition. 

For a complex system, determination of the stoichiometry of a reacting system in the form of the maximum number (R) of linearly independent chemical equations is described in Examples 1-3 and 14. This can be a useful preliminary step in a kinetics study once all the reactants and products are known. It tells us the minimum number (usually) of species to be analyzed for, and enables us to obtain corresponding information about the remaining species. We can thus use it to construct a stoichiometric table corresponding to that for a simple system in Example 2-4. Since the set of equations is not unique, the individual chemical equations do not necessarily represent reactions, and the stoichiometric model does not provide a reaction network without further information obtained from kinetics. 

By 1984, it was clear that the derivatives that arise in this DFT thermodynamics contain chemically useful information, /a is — 1 times the electronegativity. p(r) is the electron density—fundamental in its own right, but also closely related to the electrostatic potential. If, in analogy to Equation 18.6, one writes the total differential for the chemical potential,... 

A chemical equation represents a chemical change that is taking place. On the left side of the reaction arrow are the reactants, the chemical substances that are changed. On the right of the reaction arrow are the reaction products, the new substances formed. Sometimes additional information appears above or below the reaction arrow. 

To find the moles of IF5 from the limiting reagent, we need to use a mole ratio derived from information in the balanced chemical equation. (This is another place where, if we had not balanced the equation, we would be in trouble.)... 

For example, we could use this reaction for determining the concentration of acetic acid, HQHjO in vinegar. A titration problem will give you information about one reactant, and ask you for information about the other reactant. In most titration reactions, information about the products will not be necessary. You only need to consider the products when we need to balance the chemical equation. 

Let s begin with this titration question How many moles of calcium hydroxide are necessary to titrate 0.250 mol of acetic acid We have information about the acetic acid, and we are seeking information about the calcium hydroxide. We will begin the problem with the acetic acid since we know more about it, and we will end the problem with the calcium hydroxide since we do not know anything about this compound. One way to remember what you need to do is to copy the given information and the question to the balanced chemical equation, as shown here ... 

How would the problem be different if the titration question asked is How many moles of calcium hydroxide are necessary to titrate 0.0500 L of a 0.100 M acetic acid solution We can begin by adding our information to the balanced chemical equation ... 

If it was not clear before, it should be clear now, that we still must find moles. We will find moles from the mass of KC103 and the balanced chemical equation. We need to determine the molar mass of KC103 from the atomic weights of the individual elements (122.55 g/mol). We now add our mole information to the equation ... 

You should be very careful when working problems involving gases and one or more other phases. The gas laws can only give direct information about gases. This is why there is a mole ratio conversion (from the balanced chemical equation) in this example to convert from the solid (KCI03) to the gas (02). 

We will need the moles of HN02 in all the remaining steps in this problem. The moles of NaOH will be changing as we add more. The coefficients in the reaction are all ones, thus, we can simply compare the moles to find the limiting reactant. The sodium hydroxide, with the smaller number of moles is limiting. We can add the mole information to the balanced chemical equation. (The water, being neutral, will not be tracked.)... 

A balanced chemical equation provides many types of information. It shows which chemical species are the reactants and which species are the products. It may also indicate in which state of matter the reactants and products exist. Special conditions of temperature, catalysts, etc., may be placed over or under the reaction arrow. And, very importantly, the coefficients (the integers in front of the chemical species) indicate the number of each reactant that is used and the number of each product that is formed. These coefficients may stand for individual atoms/molecules or they may represent large numbers of them called moles (see the Stoichiometry chapter for a discussion of moles). The basic idea behind the balancing of equations is the Law of Conservation of Matter, which says that in ordinary chemical reactions matter is neither created nor destroyed. The number of each type of reactant atom has to equal the number of each type of product atom. This requires adjusting the reactant and product coefficients—balancing the equation. When finished, the coefficients should be in the lowest possible whole-number ratio. 

These books will teach you how to solve and balance chemical equations, find molecular weights, how to double or triple the scale of your formula (multiplying the given formula by two or three rarely works as rates of reaction and dynamic equilibrium change much more differently as the mass of reagents and precursors are increased) and other necessary information. I would like to have included this information but it would take several decades to do so and the finished book would be longer than four holy bibles combined. With so many good chemistry books available, it would be impractical for me to- do this. 

The revised edition of the Fuel Field Manual contains most of the same information as the original edition. Portions of the text have been revised to correct mistakes and to better describe some of the technological detail presented. Several schematic diagrams and chemical equations have been added to help clarify processes taking place within the refinery. Graphics depicting problems associated within the fuel injection and combustion systems are also included. 

Additional information may be included when writing a chemical equation. One common practice is to indicate the physical state of substances by use of the subscripts (s), (1), (g), (aq) to indicate solid, liquid, gas, or aqueous (dissolved in water), respectively. Hence, the combustion of carbon to form carbon dioxide would be represented as ... 

Take the needed information from Table 17-3, and use it with the balanced chemical equation... 

A properly balanced chemical equation shows all the information we have just discussed. Soluble salts and strong electrolytes in aqueous solution are always written in ionic form—for example, Na+ + n0 NaCl) or H+ 0r H30+)... 

The essential information implied hy the chemical equation is the stoichiometry at the macroscopic level, i e.. if or moles of A react, then b moles of B do also p moles of P formed, etc. 

The chemical equation for an elementary reaction is a description of an individual molecular event that involves breaking and/or making chemical bonds. By contrast, the balanced equation for an overall reaction describes only the stoichiometry of the overall process, but provides no information about how the reaction occurs. The equation for the reaction of N02 with CO, for example, does not tell us that the reaction occurs by direct transfer of an oxygen atom from an N02 molecule to a CO molecule. 

Some additional information that can be conveyed in a balanced chemical equation (s) = solid, (g) = gas, (aq) = aqueous, and (1) = liquid. The following equation shows the proper use of these symbols S(s) + 6HN03(aq) —> H2S04(aq) + 6N02(g) + 2H20(1). It should be noted that [aq] means aqueous solution and [1] means in the liquid phase of a pure substance. Use phase-indicating symbols in your balanced equation in no. 3 above. 

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