Entropy change equilibrium constant

Enthalpy, entropy, and equilibrium constant are important characteristics of CTC. The enthalpy and entropy of CTC formation are negative. The enthalpy of formation changes in a wide range. Below we present the AW", AS", and K for several complexes in n-paraffins. 

In these examples tire entropy change does not vaty widely, and the value of the equilibrium constant is mainly determined by the heat of dissociation. It can be concluded, tlrerefore, that niuogen is one of the most stable diatomic molecules, and tlrat chlorine is tire most stable diatomic halogen molecule. 

The equilibrium constant of a reaction can be related to the changes in Gibbs Free Energy (AG), enthalpy (AH) and entropy (AS) which occur during the reaction by the mathematical expressions ... 

E3.7 A block of copper weighing 50 g is placed in 100 g of HiO for a short time. The copper is then removed from the liquid, with no adhering drops of water, and separated from it adiabatically. Temperature equilibrium is then established in both the copper and water. The entire process is carried out adiabatically at constant pressure. The initial temperature of the copper was 373 K and that of the water was 298 K. The final temperature of the copper block was 323 K. Consider the water and the block of copper as an isolated system and assume that the only transfer of heat was between the copper and the water. The specific heat of copper at constant pressure is 0.389 JK. g l and that of water is 4.18 J-K 1-g 1. Calculate the entropy change in the isolated system. 

The reaction favours the formation of ozone with a significant equilibrium constant. Appendix C also lists the enthalpies of formation and the standard enthalpy of the reaction ArH° can be calculated. The answer for the enthalpy calculation is ArH° = —106.47 kJ mol, showing this to be an exothermic reaction, liberating heat. The entropy change at 298 K can also be calculated because ArG° = ArH° — T ArS°, so ArS° = 25.4 Jmol-1 K-1, indicating an increase in the entropy of the reaction as it proceeds by creating one molecule from two. 

When comparing similar or parallel reactions, consideration of the changes in Gibbs free energy A G, enthalpy AH and entropy AS can be valuable. The equilibrium constant is related to these quantities by two fundamental thermodynamic expressions... 

In the formation of activated complex, if AG, AH and AS are change in free energy, enthalpy and entropy, respectively, for one gram mole of the substance, then equilibrium constant... 

The equilibrium concentration of the ions A- and B- participating in the equlibrium can be directly observed by mass spectrometry. Thus, the free-energy change can be derived from the equilibrium constant, since the concentrations of the neutral species are known in advance. Similarly, by measuring the temperature dependence of the equilibrium constants, the associated enthalpy and entropy can be obtained from van t Hoff plots. By measuring a series of interconnecting equlibria, an appropriate scale can be established. The primary standard in such work has frequently been SO2 whose electron affinity is well established by electron photodetachment36. 

Several cases exist in which calculations of the entropy change of a reaction from values of the entropy obtained from thermal data and the third law disagree with values calculated directly from measurements of AH and determinations of AG from experimental equilibrium constants. For example, for the reaction... 

Now that we have considered the calculation of entropy from thermal data, we can obtain values of the change in the Gibbs function for chemical reactions from thermal data alone as well as from equilibrium data. From this function, we can calculate equilibrium constants, as in Equations (10.22) and (10.90.). We shall also consider the results of statistical thermodynamic calculations, although the theory is beyond the scope of this work. We restrict our discussion to the Gibbs function since most chemical reactions are carried out at constant temperature and pressure. 

Free energy changes and equilibrium constants calculated from the enthalpy and entropy values estimated by the group-contribution method generally are reliable only to the order of magnitude. For example, Andersen et al. [1] have found that their estimated enthalpies and entropies usually differ from experimental values [7]... 

Precision measurements of enthalpies of formation and entropies are probably accurate to perhaps 250 J mol and 0.8 J moF respectively. Show that either one of these uncertainties corresponds to a change of 10% in an equilibrium constant at 25°C. 

Equilibrium constants are also dependent on temperature and pressure. The temperature functionality can be predicted from a reaction s enthalpy and entropy changes. The effect of pressure can be significant when comparing speciation at the sea surface to that in the deep sea. Empirical equations are used to adapt equilibrium constants measured at 1 atm for high-pressure conditions. Equilibrium constants can be formulated from solute concentrations in units of molarity, molality, or even moles per kilogram of seawater. 

The majority of reported studies of formation of cyclodextrin inclusion complexes in solution have been mainly concerned with determination of the stability constants by using equilibrium spectroscopic techniques, and the measurement of the enthalpy and entropy changes characterizing the complexation reaction. The aim of much of this work has been to determine the driving force of complex-formation. Despite the amount of research in this area, however, no general agreement has been reached, and... 

The enthalpy value of Eq. (3.23) is very small as might be expected if two Cd-N bonds in Cd(NH3) 2 are replaced by two Cd-N bonds in Cd(en). The favorable equilibrium constants for reactions [Eqs. (3.22) and (3.23)] are due to the positive entropy change. Note that in reaction, Eq. (3.23), two reactant molecules form three product molecules so chelation increases the net disorder (i.e., increase the degrees of freedom) of the system, which contributes a positive AS° change. In reaction Eq. (3.23), the AH is more negative but, again, it is the large, positive entropy that causes the chelation to be so favored. 

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