Balanced chemical equation definition

Many of the questions in AS exams expect you to give precise definitions and correctly balanced chemical equations. These are clearly set out for you in this book. For every organic reaction, the necessary reagents and conditions are systematically included. 

Sigma (a) bonds Sigma bonds have the orbital overlap on a line drawn between the two nuclei, simple cubic unit cell The simple cubic unit cell has particles located at the corners of a simple cube, single displacement (replacement) reactions Single displacement reactions are reactions in which atoms of an element replace the atoms of another element in a compound, solid A solid is a state of matter that has both a definite shape and a definite volume, solubility product constant (/ p) The solubility product constant is the equilibrium constant associated with sparingly soluble salts and is the product of the ionic concentrations, each one raised to the power of the coefficient in the balanced chemical equation, solute The solute is the component of the solution that is there in smallest amount, solution A solution is defined as a homogeneous mixture composed of solvent and one or more solutes. 

First we interpret the balanced chemical equation to calculate the theoretical yield of CgHjN02. Then we use the actual (isolated) yield and the previous definition to calculate the percent yield. 

By definition, there must be equal numbers of equivalents of all reactants and products in a balanced chemical equation. 

Knowledge Required (1) The definition of molarity, M. (2) The interpretation of a balanced chemical equation. 

List and define all the ways of classifying chemical reactions that have been discussed in the text. Give a balanced chemical equation as an example of each type of reaction, and show clearly how your example fits the definition you have given. 

Plan We can use standard enthalpies of formation to calculate AH for the reaction. We can then use Le ChateUer s principle to determine what effect temperature will have on the equilibrium constant. Recall that the standard enthalpy change for a reaction is given by the sum of the standard molar enthalpies of formation of the products, each multipUed by its coefficient in the balanced chemical equation, less the same quantities for the reactants. At 25 C, AHj for NH3( ) is —46.19 kj/mol. The AHJ values for H2(g) and N2(g) are zero by definition, because the enthalpies of formation of the elements in their normal states at 25 C are defined as zero (S tion 5.7). Because 2 mol of NH3 is formed, the total enthalpy change is... 

After equUibrium is attained, the concentrations of products and reactants remain constant, so a ratio of their concentrations should also remain constant. The ratio of the mathematical product [C] x [D] to the mathematical product [A]" x [B]" for this reaction has a definite value at a given temperature. It is the equilibrium constant of the reaction and is designated by the letter K. The foUowing equation describes the equUib-rium constant for the hypothetical equUibrium system. The brackets ([ ]) indicate the concentration of each substance as expressed in mol/L. The superscripts are the coefficients of each substance in the balanced chemical equation. 

In Eqn. (7-1), vd and va are the stoichiometric coefficients of D and A, respectively, in the balanced chemical equation for the reaction that leads to D. With this definition, the selectivity 5(D/U) will be 1.0 (100%) when all of the A that reacts is converted into the desired product, D. If there are reactions that result in the conversion of A into compounds other than D, or reactions that result in the conversion of D into other products, then S(D/A) will be less than 1.0 (100%). Note that both the product (D) and the reactant (A) are specified in the definition of selectivity. 

Substances react according to definite ratios of numbers of particles (atoms, ions, formula units, or molecules). The following balanced chemical equation shows that two atoms of aluminum react with three molecules of iodine to form two formula units of aluminum iodide. 

Attempts to define operationally the rate of reaction in terms of certain derivatives with respect to time (r) are generally unnecessarily restrictive, since they relate primarily to closed static systems, and some relate to reacting systems for which the stoichiometry must be explicitly known in the form of one chemical equation in each case. For example, a IUPAC Commission (Mils, 1988) recommends that a species-independent rate of reaction be defined by r = (l/v,V)(dn,/dO, where vt and nf are, respectively, the stoichiometric coefficient in the chemical equation corresponding to the reaction, and the number of moles of species i in volume V. However, for a flow system at steady-state, this definition is inappropriate, and a corresponding expression requires a particular application of the mass-balance equation (see Chapter 2). Similar points of view about rate have been expressed by Dixon (1970) and by Cassano (1980). 

The definition of A/f of a substance refers to a reaction in which me mole of the substance is formed. We put one mole of C2H50H(f) on the right side of the chemical equation and put the appropriate elements in their standard states on the left. We balance the equation without chan ng the coefficient of the product, even if we must use fractional coefficients on the left. 

In lesson C the student must know the definition of molarity and moles, the quantitative relationship of a chemical equation to determine quantities of reactants and products for reactions. Lesson D has the following objectives Assignment of oxidation numbers to elements according to a set of rules balancing oxidation-reduction equations by the half-reaction method and identification of oxidizing and reducing agents. 

The balanced stoichiometric equation for a reaction tells us that the various chemical species are formed or consumed in fixed proportions. This idea is expressed mathematically by the Law of Definite Proportions. For a single reaction. 

Stoichiometric Ratio In fuel cell parlance, the term stoichiometry is defined as the inverse of the Faradic efficiency. Smdents may be confused with this terminology, since the stoichiometric condition typically describes a balanced chemical reaction equation with no excess oxidizer. Here, the term stoichiometry is used slightly differently, and its meaning is similar to the definition of equivalence ratio used in combustion. Unlike chemical reactions, the reduction and oxidation reactions are separated by electrolyte, so each electrode can have a discrete stoichiometry ... 

DEFINITION OF CHEMICAL REACTIONS AND BALANCING OF CHEMICAL EQUATIONS... 

One molecule (or mole) of propane reacts with five molecules (or moles) of oxygen to produce three molecules (or moles) or carbon dioxide and four molecules (or moles) of water. These numbers are called stoichiometric coefficients (v.) of the reaction and are shown below each reactant and product in the equation. In a stoichiometrically balanced equation, the total number of atoms of each constituent element in the reactants must be the same as that in the products. Thus, there are three atoms of C, eight atoms of H, and ten atoms of O on either side of the equation. This indicates that the compositions expressed in gram-atoms of elements remain unaltered during a chemical reaction. This is a consequence of the principle of conservation of mass applied to an isolated reactive system. It is also true that the combined mass of reactants is always equal to the combined mass of products in a chemical reaction, but the same is not generally valid for the total number of moles. To achieve equality on a molar basis, the sum of the stoichiometric coefficients for the reactants must equal the sum of v. for the products. Definitions of certain terms bearing relevance to reactive systems will follow next. 

Each of these dissociation reactions also specifies a definite equilibrium concentration of each product at a given temperature consequently, the reactions are written as equilibrium reactions. In the calculation of the heat of reaction of low-temperature combustion experiments the products could be specified from the chemical stoichiometry but with dissociation, the specification of the product concentrations becomes much more complex and the s in the flame temperature equation [Eq. (1.11)] are as unknown as the flame temperature itself. In order to solve the equation for the n s and T2, it is apparent that one needs more than mass balance equations. The necessary equations are found in the equilibrium relationships that exist among the product composition in the equilibrium system. 

To evaluate die position of the equilibrium, p is determined by the equation pAeq = pA a (reactant acid) —pAa (product acid). For the above example pA), = 17 — 10 = 7, and based on the definition of pA, Aeq = 10 7 for this equilibrium. Thus the equilibrium lies far to the reactant side that is, very litde isopropoxide ion or ethyl ammonium ion is present at equilibrium. This technique is applicable for virtually any acid-base equilibrium. The three required steps are to (a) write a balanced equation that describes the equilibrium to be analyzed, (b) identify the species which is acting as an acid on each side of the equilibrium and write down its pAa, and (c) subtract the pAa of the product acid from the pAa of the reactant acid to give the pAeq for the equilibrium in question. It is a requirement that the pAy s of the acids on each side of the equilibrium are known or can be estimated reasonably well. Furthermore, the pA eq that is determined refers to the equilibrium in the direction it is written. It is therefore important to write the chemical equilibrium as you wish to analyze it. 

Inst as compounds have definite ratios of elements, chemical reactions have definite ratios of reactants and products. Those ratios are used in Section 10.1 to calcnlate the number of moles of other substances in a reaction from the nnm-ber of moles of any one of the snbstances. Section 10.2 combines information from Section 10.1, Chapter 7, and elsewhere to explain how to calcnlate the mass of any substance involved in a reaction from the mass of another. Section 10.3 demonstrates how to work with qnantities in nnits other than moles or masses when finding quantities of reactants or prodncts. Section 10.4 shows how to calcnlate the quantities of snbstances involved in a reaction even if the quantities of reactants present are not in the mole ratio of the balanced equation. Section 10.5 covers the calculation of the percentage yield of a product from the actual yield and the theoretical yield, based on the amonnt(s) of reactant(s). Section 10.6 explains which of these types of calcnlations can and cannot be done with net ionic equations. 

In the operator L, the first term represents convection and the second diffusion. Equation (44) therefore describes a balance of convective, diffusive, and reactive effects. Such balances are very common in combustion and often are employed as points of departure in theories that do not begin with derivations of conservation equations. If the steady-flow approximation is relaxed, then an additional term, d(p(x)/dt, appears in L this term represents accumulation of thermal energy or chemical species. For species conservation, equations (48) and (49) may be derived with this generalized definition of L, in the absence of the assumptions of low-speed flow and of a Lewis... 

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