Equilibrium position temperature effects

O When an exothermic reaction is at equilibrium what effect does increasing the temperature have on the equilibrium position What effect does increasing the temperature have on the equilibrium constant ... 

Equation (Bl.8.6) assumes that all unit cells really are identical and that the atoms are fixed hi their equilibrium positions. In real crystals at finite temperatures, however, atoms oscillate about their mean positions and also may be displaced from their average positions because of, for example, chemical inlioniogeneity. The effect of this is, to a first approximation, to modify the atomic scattering factor by a convolution of p(r) with a trivariate Gaussian density function, resulting in the multiplication ofy ([Pg.1366]

As shown in Section 16-1. varies with temperature in a way that can be understood using the principles of thermod namics. Temperature is the only variable that causes a change In the value of. eq. The effect of temperature on depends on the enthalpy change of the reaction, ZlH. An increase in temperature always shifts the equilibrium position in the endothermic direction, and a decrease in temperature always shifts the equilibrium position in the exothermic direction. 

When Wqi / Wq2 the magnetization recovery may appear close to singleexponential, but the time constant thereby obtained is misleading [50]. The measurement of 7) of quadrupolar nuclei under MAS conditions presents additional complications that have been discussed by comparison to static results in GaN [50]. The quadrupolar (two phonon Raman) relaxation mechanism is strongly temperature dependent, varying as T1 well below and T2 well above the Debye temperature [ 119]. It is also effective even in cases where the static NQCC is zero, as in an ideal ZB lattice, since displacements from equilibrium positions produce finite EFGs. 

Many thermal reactions are effectively irreversible under the conditions employed, but some are reversible and an equilibrium position is reached between substrates and products. The position of equilibrium depends on the standard free energy difference between the two (AC - = - RT In K and on reagent concentrations, and A varies with temperature. Such considerations rarely apply to photochemical reactions, the overwhelming maiority of which are effectively irreversible (1.3), and the products are not in thermodynamic... 

Anisothermal Transport Across a Phase Boundary. Once we know the effect of temperature on equilibrium position, we need know only its effects on diffusivities and the condensation coefficient to complete our task. The Stephan-Maxwell equation states that diffusivity in the vapor increases with the square root of the absolute temperature. In the condensed phase the temperature effect is expressed by an Arrhenius-type equation. 

A catalyst affects only the rate of a chemical reaction it has no effect on Ke 0r on the position of equilibrium at a given temperature. You cannot, therefore, increase the yield of a chemical reaction at a given temperature by adding a catalyst to the reaction mixture. Catalysts are, however, of great practical value because they may make an impractically slow reaction reach equilibrium at a practical rate, or may permit such a reaction to go at a practical rate at a lower temperature, where a more favorable equilibrium position exists. 

Figure 14.4. Less common examples of ternary equilibria and some temperature effects, (a) The system 2,2,4-tri-methylpentane + nitroethane + perfluorobutylamine at 25°C the Roman numerals designate the number of phases in that region [Vreeland and Dunlap, J. Phys. Chem. 61, 329 (1957)]. (b) Same as (a) but at 51.3°C. (c) Glycol + dodecanol + nitroethane at 24°C 12 different regions exist at 14°C [Francis, J. Phys. Chem. 60, 20 (1956)]. (d) Docosane + furfural + diphenylhexane at several temperatures [Varteressian and Fenske, Ind. Eng. Chem. 29, 270 (1937)]. (e) Formic acid + benzene + tribromomethane at 70°C the pair formic acid/benzene is partially miscible with 15 and 90% of the former at equilibrium at 25°C, 43 and 80% at 70°C, but completely miscible at some higher temperature, (f) Methylcyclohexane + water + -picoline at 20°C, exhibiting positive and negative tieline slopes the horizontal tieline is called solutropic (Landolt-Bornstein II2b).

The preceding considerations are restricted to the case of zero temperature. To understand the role of the temperature, we now evaluate the effect of thermal fluctuations on the equilibrium position of the tube. 

Forward reaction (left to right) Change in temperature Effect on position of equilibrium... 

We can qualitatively predict the effects of changes in concentration, pressure, and temperature on a system at equilibrium by using Le Chatelier s principle, which states that if a change in conditions (a stress ) is imposed on a system at equilibrium, the equilibrium position unll shift in a direction that tends to reduce that change in conditions. Although this rule, put forth by Henri Le Chatelier in 1884, sometimes oversimplifies the situation, it works remarkably well. 

The fourth major parameter which defines a system after the monomer, the initiator(s) and the solvent, is the temperature at which the polymerisation is conducted. The effect of temperature upon the position of the propagation-depropa tion equilibrium (ceiling temperature) is not directly relevant and too well-known to be discus here. We are obviously more interested in discussing the specific role of temperature in the reactions leading to the formation of chain carriers. The following considerations are pertinent to the kinetics of such interactions and to the thermodynamics of the reailting equflibria. 

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