Equilibrium constants meaning

D—The low value for the equilibrium constant means that the equilibrium lies to the left. For this to be true, the weaker acid and the weaker base must be on the left side. 

A quantitative measure of the degree of dissociation is given by the equilibrium constant for the acid or base. The higher the equilibrium constant is, the greater the percent dissociation of the acid or base. Therefore, a higher equilibrium constant means a stronger acid or base. Equilibrium constants, K and K, are listed for several com-mon weak acids and bases in Table 13.4. 

According to equation (5) the equilibrium constant of a gaseous reaction increases with temperature, if AH is positive. An increase in the equilibrium constant means an increase in the proportion of the resultants, so that if heat is absorbed in the reaction, an increase in temperature favours the formation of the resultants. On considering the reverse case, if heat is evolved in the reaction, an increase of temperature displaces the equilibrium in the direction of the reactants. The behaviour is again in accordance with the Le-Chatelier s principle. 

This low value of the equilibrium constant means that when equilibrium is attained in the ferrous-ferric and stannous-stannic mixture, the concentrations (activities) of ferric and stannous ions must be negligibly small in comparison with those of the ferrous and stannic ions. In other words, when these two systems are mixed, reaction occurs so that the ferric ions are virtually completely reduced to ferrous ions while the stannous are oxidized to stannic ions. This fact is utilized in analytical work for the reduction of ferric to ferrous ions prior to the estimation of the latter by means of dichromate. 

A small equilibrium constant means that at equilibrium the concentration of the products is small compared with the concentration of reactants. The position of equilibrium lies far to the left. A reaction with a small equilibrium constant is therefore not useful as a means of producing the products. To become useful, the equilibrium position would have to be shifted to the right. 

The very large equilibrium constant means that the oxidation of Zn by Cu is virtually complete. 

SECTION 15.3 The value of the equilibrium constant changes with temperature. A large value of indicates that the equilibrium mixture contains more products than reactants and therefore lies toward the product side of the equation. A small value for the equilibrium constant means that the equilibrium mixture contains less products than reactants and therefore lies toward the reactant side. The equilibrium-constant expression and the equilibrium constant of the reverse of a reaction are the reciprocals of those of the forward reaction. If a reaction is the sum of two or more reactions, its equilibrium constant will be the product of the equilibrium constants for the individual reactions. 

FIGURE 15.6 The meaning of a large equilibrium constant A large equilibrium constant means that there will be a high concentration of products and a low concentration of reactants at equilibrium. 

In this chapter, we have learned that the equilibrium constant describes the ultimate fate of a chemical reaction. Large equilibrium constants mean that the reaction favors the products. Small equilibrium constants mean that the reaction Warning Hydrogen gas is explosive and ors the reactants. But the equilibrium constant by itself does not teU the whole... 

Here you denote the molar concentration of a substance by writing its formula in square brackets. The subscript c on the equilibrium constant means that it is defined in terms of molar concentrations. The law of mass action is a relation that states that the values of the equilibrium-constant expression Kc are constant for a particular reaction at a given temperature, whatever equilibrium concentrations are substituted. ... 

A large value for the equilibrium constant means that the rate constant for the forward reaction is large compared with the rate constant for the reverse reaction. A small value means that the rate constant for the forward reaction is small compared with the rate constant for the reverse reaction. Equation (11.4-4) can apply to a more general case if orders are equal to stoichiometric coefficients, as shown in the following exercise ... 

The comparison of the experimental mean values with the theoretically calculated ones for individual tautomers (Section 4.04.1.5.1) (76AHC(S1)1) or conformers (Section 4.04.1.4.3) has been used in the literature to determine equilibrium constants. Thus, the experimental value for l,l -thiocarbonylbis(pyrazole) (40) is 3.19 D and the vector sums of the simple group moments after addition of the extra mesomeric moments are shown in Figure 8. From these values Carlsson and Sandstrom (6SACS1655) concluded that conformation (40b) exerts the largest influence. 

The mean chemical shifts of A- unsubstituted pyrazoles have been used to determine the tautomeric equilibrium constant, but the method often leads to erroneous conclusions (76AHC(Sl)l) unless the equilibrium has been slowed down sufficiently to observe the signals of individual tautomers (Section 4.04.1.5.1). When acetone is used as solvent it is necessary to bear in mind the possibility (depending on the acidity of the pyrazole and the temperature) of observing the signals of the 1 1 adduct (55) whose formation is thermodynamically favoured by lowering the solution temperature (79MI40407). A similar phenomenon is observed when SO2 is used as solvent. 

The overall rate being measured is that of step 2, but there may be no means of directly measuring [ROH2+]. The concentration of the protonated intermediate ROH2+ can be expressed in terms of the concentration of the starting material by taking into consideration the equilibrium constant, which relates [ROH], [Br ], and [H+] ... 

The solution then follows along the same lines as for TCR if the temperature and pressure are known then 7, S and the resulting mole fractions can be determined from the equilibrium constants. The temperature change between inlet and outlet is now likely to be higher than in the TCR reactions, so the determination of the A, s as functions of a single mean temperature for the reaction is more difficult. 

If the rate equation contains the concentration of a species involved in a preequilibrium step (often an acid-base species), then this concentration may be a function of ionic strength via the ionic strength dependence of the equilibrium constant controlling the concentration. Therefore, the rate constant may vary with ionic strength through this dependence this is called a secondary salt effect. This effect is an artifact in a sense, because its source is independent of the rate process, and it can be completely accounted for by evaluating the rate constant on the basis of the actual species concentration, calculated by means of the equilibrium constant appropriate to the ionic strength in the rate study. 

It is reasonable to expeet that models in ehemistry should be capable of giving thermodynamic quantities to chemical accuracy. In this text, the phrase thermodynamic quantities means enthalpy changes A//, internal energy changes AU, heat capacities C, and so on, for gas-phase reactions. Where necessary, the gases are assumed ideal. The calculation of equilibrium constants and transport properties is also of great interest, but I don t have the space to deal with them in this text. Also, the term chemical accuracy means that we should be able to calculate the usual thermodynamic quantities to the same accuracy that an experimentalist would measure them ( 10kJmol ). 

Similar, although less well documented, is Bryson s observation that a constant term must occasionally be included in the Hammett equation, i.e. A K = ap +a, which means that the intercept is significantly different from the equilibrium constant for the parent compound. 

This means that, with increasing length of chain, the equilibrium constants K1 and K2 (the first and second dissociation constants at infinite dilution of the acid) should not tend to equality rather their ratio K1/K2 should tend toward the value 4, as recognized by Adams.1... 

Because XL.q is relatively large, the reaction proceeds as written and greater than 99.999 99% of the ethylene is converted into bromoethane. For practical purposes, an equilibrium constant greater than about 103 means that the amount of reactant left over will be barely detectable (less than 0.1%). 

What typically happens for an energetically unfavorable reaction to occur is that it is "coupled" to an energetically favorable reaction so that the overall free-energy change for the two reactions together is favorable. To understand what it means for reactions to be coupled, imagine that reaction 1 does not occur to any reasonable extent because il has a small equilibrium constant and is energetically unfavorable that is, the reaction has AG > 0. 

Attempts to determine the equilibrium constant for Equation (60), applying the method proposed by Fialkov [313] for an AB2 = A+2B type interaction, provided values that defy physical logic. This means that the equilibrium in Equation (60) shifts almost completely to the left, and that it is also disturbed by A + B = AB type interactions [313], which, in this case, correspond to the interaction F" + TaFs = TaF6". Due to the improbability of the presence of TaF5 in the melts, it makes more sense to attribute the TaFg ions to the equilibrium described in Equation (61), which provides an analogical effect on the additive values of the property. 

Now look at the numerical values of the equilibrium constants. The K s listed range from 10+1 to 10 16, so we see there is a wide variation. We want to acquire a sense of the relation between the size of the equilibrium constant and the state of equilibrium. A large value of K must mean that at equilibrium there are much larger concentrations present of products than of reactants. Remember that the numerator of our equilibrium expression contains the concentrations of the products of the reaction. The value of 2 X 10,s for the K for reaction (19) certainly indicates that if a reaction is initiated by placing metallic copper in a solution containing Ag+ (for example, in silver nitrate solution), when equilibrium is finally reached, the concentration of Cu+2 ion, [Cu+2], is very much greater than the square of the silver ion concentration, [Ag+]2. 

Solubility equilibrium constants, such as (20) and (22), are given a special name—the solubility product. It is symbolized K,p. A low value of K,p means the concentrations of ions are low at equilibrium. Hence the solubility must be low. Table 10-11 lists solubility products for some common compounds. 

Electrochemical Method.—In this the value of the equilibrium constant K is calculated from the maximum work measured by means of the electromotive force of a voltaic cell (cf. Chap. XVI.). 

If the equilibrium constant is calculated with activity constants derived from Raoul s law instead of concentrations, then K is virtually independent of the water concentration.30 The reported values of AHa for hydrolytic polyamidation are in the order of 25-29 kJ mol-1.29 This means that on decreasing the temperature at a constant water concentration, the equilibrium molecular weight shifts to a higher value. 

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