Chemical equations coefficients

The value of K has no dimensions because the concentrations are actually approximations for a dimensionless quantity called an activity. The law of mass action is good for all chemical equations, including non-elementary equations. In other words, for equilibrium constants, use the chemical equation coefficients as the exponents of the concentrations regardless of molecularity. Notice that the equilibrium constant is a capital K and the rate constant is represented by lowercase k. Also notice that the equilibrium constant for the reverse reaction is the reciprocal of the equilibrium constant of the forward reaction. This is true regardless of whether or not the reaction is elementary. Following this same line of reasoning will demonstrate that the equilibrium constant for a series of reactions is equal to the product of the equilibrium constants for each of its elementary steps. Since the rate constant depends upon temperature, the equilibrium constant must also depend upon temperature. 

The number written in front of the chemical formulas in a balanced chemical equation— coefficients indicate the relative numbers of reactants and products in the reaction. 

Using Chemical Equation Coefficients a Factors (Mass to Mas ... 

Using Chemical Equation Coefficients as Conversion Factors (Moles to Moles)... 

The rate of a process is expressed by the derivative of a concentration (square brackets) with respect to time, d[ ]/dt. If the concentration of a reaction product is used, this quantity is positive if a reactant is used, it is negative and a minus sign must be included. Also, each derivative d[ ]/dt should be divided by the coefficient of that component in the chemical equation which describes the reaction so that a single rate is described, whichever component in the reaction is used to monitor it. A rate law describes the rate of a reaction as the product of a constant k, called the rate constant, and various concentrations, each raised to specific powers. The power of an individual concentration term in a rate law is called the order with respect to that component, and the sum of the exponents of all concentration terms gives the overall order of the reaction. Thus in the rate law Rate = k[X] [Y], the reaction is first order in X, second order in Y, and third order overall. 

A mechanism is a series of simple reaction steps which, when added together, account for the overall reaction. The rate law for the individual steps of the mechanism may be written by inspection of the mechanistic steps. The coefficients of the reactants in the chemical equation describing the step become the exponents of these concentrations in the rate law for... 

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. 

Throughout Section 11.3, balanced chemical equations are written in such a way that the coefficient of die reactant is 1. In general, if the coefficient of the reactant is a, where a may be 2 or 3 or..., then k in each integrated rate equation must be replaced by the product ak. (See Problem 101.)... 

The equilibrium constant expression for the dissolving of SrCr04 can be written following the rules in Chapters 12 and 13. In particular, the solid does not appear in the expression the concentration of each ion is raised to a power equal to its coefficient in the chemical equation. 

Clausius-Clapeyron equation An equation expressing the temperature dependence of vapor pressure ln(P2/Pi) = AHvapCl/Tj - 1/T2)/R, 230,303-305 Claussen, Walter, 66 Cobalt, 410-411 Cobalt (II) chloride, 66 Coefficient A number preceding a formula in a chemical equation, 61 Coefficient rule Rule which states that when the coefficients of a chemical equation are multiplied by a number n, the equilibrium constant is raised to the nth power, 327... 

Such expressions are called chemical equations. Notice that we show two molecules of a substance by writing the coefficient 2 before the... 

Equation (7) is also a chemical equation—again atoms are conserved. It is just as correct an expression for the burning of magnesium as is (6). To show this, we can multiply (7) by 2 to obtain equation (6). We can always multiply all the coefficients by a common factor or divide by a common factor and obtain equally valid equations. 

In each step, we may need to reverse the equation or multiply it by a factor. Recall from Eq. 16 that, if wc want to reverse a chemical equation, wc have to change the sign of the reaction enthalpy. If we multiply the stoichiometric coefficients by a factor, we must multiply the reaction enthalpy by the same factor. 

Now there are four H atoms, two Na atoms, and two O atoms on each side, and the equation conforms to the law of conservation of mass. The number multiplying an entire chemical formula in a chemical equation (for example, the 2 multiplying H20) is called the stoichiometric coefficient of the substance. A coefficient of 1 (as for H2) is not written explicitly. 

In other words, the stoichiometric coefficients multiplying the chemical formulas in any balanced chemical equation tell us the relative number of moles of each substance that reacts or is produced in the reaction. 

A balanced chemical equation symbolizes both the qualitative and the quantitative changes that take place in a chemical reaction. The stoichiometric coefficients tell us the relative numbers of moles of reactants and products taking part in the reaction. 

Although normally the coefficients in a balanced chemical equation are the smallest possible whole numbers, a chemical equation can be multiplied through by a factor and still be a valid equation. At times it is convenient to use fractional coefficients for example, we could write... 

A chemical equation expresses a chemical reaction in terms of chemical formulas the stoichiometric coefficients are chosen to show that atoms are neither created nor destroyed in the reaction. 

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... 

Step 2 Use the mole ratio derived from the stoichiometric coefficients in the balanced chemical equation to convert from the amount of one substance (A) into the amount in moles of the other substance (B). For aA - / B or aA + hY> — cC, use... 

Because the stoichiometric coefficient of C6H6 in the chemical equation is 2, calculate AH for 2 mol CbHb from AH = q X (2 mol)/ . Because the reaction is exothermic, AH is negative. 

STRATEGY We write the chemical equation for the formation of HI(g) and calculate the standard Gibbs free energy of reaction from AG° = AH° — TAS°. It is best to write the equation with a stoichiometric coefficient of 1 for the compound of interest, because then AG° = AGf°. The standard enthalpy of formation is found in Appendix 2A. The standard reaction entropy is found as shown in Example 7.9, by using the data from Table 7.3 or Appendix 2A. 

The equilibrium composition of a reaction mixture is described by the equilibrium constant, which is equal to the activities of the products (raised to powers equal to their stoichiometric coefficients in the balanced chemical equation for the reaction) divided by the activities of the reactants (raised to powers equal to their stoichiometric coefficients). 

We can summarize these remarks as follows for chemical equations written with the smallest whole-number stoichiometric coefficients (Fig. 9.5) ... 

The powers to which the activities are raised in the expression for an equilibrium constant must match the stoichiometric coefficients in the chemical equation, which is normally written with the smallest whole numbers for coefficients. Therefore, if we change the stoichiometric coefficients in a chemical equation (for instance, by... 

The value of E is the same, regardless of how we write the equation, but the value of AG° depends on the stoichiometric coefficients in the chemical equation. When we multiply all the coefficients by 2 the value of AG° doubles. However, multiplying all the coefficients by 2 also doubles the value of n, and so E° = AG°/nF remains the same. That is, although the reaction Gibbs free energ) changes when the chemical equation is multiplied by a factor, E° does not change ... 

Calculate the reaction quotient, Q, for the cell reaction, given the measured values of the cell emf. Balance the chemical equations by using the smallest whole-number coefficients. 

Division by the stoichiometric coefficients takes care of the stoichiometric relations between the reactants and products. There is no need to specify the species when reporting the unique average reaction rate, because the value of the rate is the same for each species. However, the unique average rate does depend on the coefficients used in the balanced equation, and so the chemical equation should be specified when reporting the unique rate. 

A note on good practice The chemical equations for elementary reaction steps are written without the state symbols. They differ from the overall chemical equation, which summarizes bulk behavior, because they show how individual atoms and molecules take part in the reaction,. We do not use stoichiometric coefficients for elementary reactions. Instead, to emphasize that we are depicting individual molecules, we write the formula as many times as required. 

Gibbs free energy of reaction The difference in molar Gibbs free energies of the products and reactants, weighted by the stoichiometric coefficients in the chemical equation. 

Stem-Gerlach experiment The demonstration of the quantization of electron spin by passing a beam of atoms through a magnetic field, stick structure See line structure. stock solution A solution stored in concentrated form, stoichiometric coefficients The numbers multiplying chemical formulas in a chemical equation. 

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