Chemical equations products from

Sometimes we need to know how much product to expect from a reaction, or how much reactant we need to make a desired amount of product. The quantitative aspect of chemical reactions is the part of chemistry called reaction stoichiometry. The key to reaction stoichiometry is the balanced chemical equation. Recall from Section H that a stoichiometric coefficient in a chemical equation tells us the relative amount (number of moles) of a substance that reacts or is produced. Thus, the stoichiometric coefficients in... 

A chemist who carries out a reaction in the laboratory needs to know how much product can be obtained from a given amount of starting materials (reactants). To do this, he or she starts by writing a balanced chemical equation. 

Beginning students are sometimes led to believe that writing a chemical equation is a simple, mechanical process. Nothing could be further from the truth. One point that seems obvious is often overlooked. You cannot write an equation unless you know what happens in the reaction that it represents. All the reactants and all the products must be identified. Moreover, you must know their formulas and physical states. 

As pointed out in Chapter 2, when an ionic solid dissolves in water, the cations and anions separate from each other. This process can be represented by a chemical equation in which the reactant is the solid and the products are the positive and negative ions in water (aqueous) solution. For the dissolving of MgCl2, the equation is... 

In this generalized equation, (75), we see that again the numerator is the product of the equilibrium concentrations of the substances formed, each raised to the power equal to the number of moles of that substance in the chemical equation. The denominator is again the product of the equilibrium concentrations of the reacting substances, each raised to a power equal to the number of moles of the substance in the chemical equation. The quotient of these two remains constant. The constant K is called the equilibrium constant. This generalization is one of the most useful in all of chemistry. From the equation for any chemical reaction one can immediately write an expression, in terms of the concentrations of reactants and products, that will be constant at any given temperature. If this constant is measured (by measuring all of the concentrations in a particular equilibrium solution), then it can be used in calculations for any other equilibrium solution at that same temperature. 

L.25 Barium bromide, BaBrv, can be converted into BaCl2 by treatment with chlorine. It is found that 3.25 g of BaBrv reacts completely with an excess of chlorine to yield 2.27 g of BaCl2. Determine the value of x and write the balanced chemical equation for the production of BaCl2 from BaBr,.. 

STRATEGY First, we write the chemical equation for the equilibrium and the expression for the solubility product. To evaluate Ksp, we need to know the molarity of each type of ion formed by the salt. We determine the molarities from the molar solubility, the chemical equation for the equilibrium, and the stoichiometric relations between the species. We assume complete dissociation. 

We stressed in Section 13.3 that we cannot in general write a rate law from a chemical equation. The reason is that all but the simplest reactions are the outcome of several, and sometimes many, steps called elementary reactions. Each elementary reaction describes a distinct event, often a collision of particles. To understand how a reaction takes place, we have to propose a reaction mechanism, a sequence of elementary reactions describing the changes that we believe take place as reactants are transformed into products. 

A reaction mechanism is a series of simple molecular processes, such as the Zeldovich mechanism, that lead to the formation of the product. As with the empirical rate law, the reaction mechanism must be determined experimentally. The process of assembling individual molecular steps to describe complex reactions has probably enjoyed its greatest success for gas phase reactions in the atmosphere. In the condensed phase, molecules spend a substantial fraction of the time in association with other molecules and it has proved difficult to characterize these associations. Once the mecharrism is known, however, the rate law can be determined directly from the chemical equations for the individual molecular steps. Several examples are given below. 

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 ... 

Figure 48-12. Schematic illustration of some aspects of the role of the osteoclast in bone resorption. Lysosomal enzymes and hydrogen ions are released into the confined microenvironment created by the attachment between bone matrix and the peripheral clear zone of the osteoclast. The acidification of this confined space facilitates the dissolution of calcium phosphate from bone and is the optimal pH for the activity of lysosomal hydrolases. Bone matrix is thus removed, and the products of bone resorption are taken up into the cytoplasm of the osteoclast, probably digested further, and transferred into capillaries. The chemical equation shown in the figure refers to the action of carbonic anhydrase II, described in the text. (Reproduced, with permission, from Jun-queira LC, Carneiro J BasicHistology. Text Atlas, 10th ed. McGraw-Hill, 2003.)...

Entropy changes are important in every process, but chemists are particularly interested in the effects of entropy on chemical reactions. If a reaction occurs under standard conditions, its entropy change can be calculated from absolute entropies using the same reasoning used to calculate reaction enthalpies from standard enthalpies of formation. The products of the reaction have molar entropies, and so do the reactants. The total entropy of the products is the sum of the molar entropies of the products multiplied by their stoichiometric coefficients in the balanced chemical equation. The total entropy of the reactants is a similar sum for the reactants. Equation... 

A chemical equation shows that as a chemical reaction takes place, reactants are changed into products. The reaction rate of a chemical reaction is often expressed as the change in concentration of a reactant or a product in a unit amount of time. In this activity, the reaction rate will be calculated from the amount of time it takes for a given amount of magnesium (Mg) to react completely with hydrochloric acid (HCI). 

The formation of a cyclopropanone derivative (originally determined by the isolation of degradation products from this unstable species) stimulated considerable interest in this reaction. Tetramethylcyclopropanone, however, cannot be isolated from the reaction mixture under normal photolysis conditions even with the use of an inert solvent. That it is indeed formed as an initial product of a-cleavage results from various trapping experiments in which chemical agents present in the reaction mixture were used to produce stable derivatives of the cyclopropanone [see equation (4.65)]. 

Before you can balance a chemical equation, you have to know the formulas for all the reactants and products. If the names are given for these substances, you have to know how to write formulas from the names (Chap. 6). If reactants only are given, you have to know how to predict the products from the reactants. This latter topic is the subject of this section. 

A combination reaction is a reaction of two reactants to produce one product. The simplest combination reactions are the reactions of two elements to form a compound. After all, if two elements are treated with each other, they can either react or not. There is no other possibility, since neither can decompose. In most reactions like this, there will be a reaction. The main problem is to write the formula of the one product correctly, and then balance the equation. In this process, first determine the formulas of the products from the rules of chemical combination (Chap. 5). Only when the formulas of the reactants and products have all been written down do you balance the equation by adjusting the coefficients. 

Since the balanced chemical equation also relates the numbers of formula units of reactants and products, the problem can be solved by converting directly with the factor label from the balanced equation ... 

The effect of pressure on chemical equilibria and rates of reactions can be described by the well-known equations resulting from the pressure dependence of the Gibbs enthalpy of reaction and activation, respectively, shown in Scheme 1. The volume of reaction (AV) corresponds to the difference between the partial molar volumes of reactants and products. Within the scope of transition state theory the volume of activation can be, accordingly, considered to be a measure of the partial molar volume of the transition state (TS) with respect to the partial molar volumes of the reactants. Volumes of reaction can be determined in three ways (a) from the pressure dependence of the equilibrium constant (from the plot of In K vs p) (b) from the measurement of partial molar volumes of all reactants and products derived from the densities, d, of the solution of each individual component measured at various concentrations, c, and extrapolation of the apparent molar volume 4>... 

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. 

This balanced equation can be read as 4 iron atoms react with 3 oxygen molecules to produce 2 iron(III) oxide units. However, the coefficients can stand not only for the number of atoms or molecules (microscopic level) but they can also stand for the number of moles of reactants or products. So the equation can also be read as 4 mol of iron react with 3 mol of oxygen to produce 2 mol ofiron(III) oxide. In addition, if we know the number of moles, the number of grams or molecules may be calculated. This is stoichiometry, the calculation of the amount (mass, moles, particles) of one substance in the chemical equation from another. The coefficients in the balanced chemical equation define the mathematical relationship between the reactants and products and allow the conversion from moles of one chemical species in the reaction to another. 

Convert the masses of the reactants and products to moles using their molar masses. Using the mole ratios from the balanced chemical equation, it is possible to determine how much material should react or be produced. These calculated values can be compared to the observed values. 

The reaction of calcium carbide with water yields two products. One is ethyne gas (C2H2). From your observation in step 6, suggest what the other product is, and write a balanced chemical equation for the reaction. 

Multiply each AHf value by its molar coefficient from the balanced chemical equation. Substitute into the following equation, and then solve. AH° = l,(nAHf products) - X(nAH°t reactants)... 

Chemical reactions are like factories, where goods (products) are created from raw materials (reactants). An assembly line, like the one shown in Figure 6.16, involves many steps. An automobile is not formed from its components in just one step. Similarly, most chemical reactions do not proceed immediately from products to reactants. They take place via a number of steps. While you can go inside a factory to see all the steps that are involved in maldng an automobile or a piece of clothing, you cannot observe a chemical equation on a molecular scale as it proceeds. Chemists can experimentally determine the reactants and products of a reaction, but they must use indirect evidence to suggest the steps in-between. 

Name another possible carbon-containing product from the incomplete combustion of methane. Write a balanced chemical equation for this reaction. 

The zinc anode and copper cathode of a Daniell cell are both metals, and can act as electrical conductors. However, some redox reactions involve substances that cannot act as electrodes, such as gases or dissolved electrolytes. Galvanic cells that involve such redox reactions use inert electrodes. An inert electrode is an electrode made from a material that is neither a reactant nor a product of the cell reaction. Figure 11.6 shows a cell that contains one inert electrode. The chemical equation, net ionic equation, and half-reactions for this cell are given below. 

Example 2.10. Probably the best contemporary example of a variable-mass system would be the equations of motion for a space rocket whose mass decreases as fuel is consumed. However, to stick with chemical engineering systems, let us consider the problem sketched in Fig. 2.8. Petroleum pipelines are sometimes used for transferring several products from one location to another on a batch basis, i.e., one product at a time. To reduce product contamination at the end of a batch transfer, a leather ball or pig that just fits the pipe is inserted in one end of the hne. Inert gas is introduced behind the pig to push it through the hne, thus purging the hne of whatever hquid is in it. 

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