Effect of temperature on activity

To determine the effect of temperature on r ,. we start with equation (6.84) and divide by T to get 

We use the Gibbs-Helmholtz relationship to obtain the derivatives on the left 

In defining the activity through equations (6.83) and (6.84), we have made no restrictions on the choice of a standard state except to note that specification of temperature is not a part of the standard state condition. We are free to choose standard states in whatever manner we desire.p However, choices are usually made that are convenient and simplify calculations involving activities. The usual choices differ for a gas, pure solid or liquid, and solvent or solute in solution. We will now summarize these choices of standard states and indicate the reasons. Before doing so, we note that activities for a substance with different choices of standard states are proportional to one another. This can be seen as follows With a particular choice of standard state 

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Fig. 1. Effect of temperature on activity of soluble invertase ( ) and Dowex-lx4-200/invertase complex (O).

Effect of Temperature on Activation. The extent of activation is a function of temperature as shown in Figure 4, a linear relationship is disclosed when log Kx is plotted against 1/T, but it is not yet known... 

The effect of temperature on ion activity coefficients is largely predicted by changes in the value of A, which is proportional to - log y, in the Debye-Huckel equation. The value of A increases from 0.492 to 0.534 between 0 and 50°C. Thus, activity coefficients become smaller with increasing temperature. Because A is multiplied by z in the Debye-Hiickel equation, the effect of temperature on activity coefficients is greatest for multivalent ions. 

A plot of electrode potential against pH at different temperature shows the effect of temperature on activity and should be corrected (Fig. 4). 

Coyer, P. E., and Mangum, C. P. (1973). Effect of temperature on active and resting metabolism in polychaetes. In Effects of Temperature on Ectothermic Organisms (W. Wieser, ed.), pp. 173-180. Springer-Verlag, Berlin and New York. 

The effect of temperature on activity and selectivity was studied in decane solvent in the teirperature range of 20 - 70°C with the 5% Rh/C catalyst at 10 bar. The results presented in Table 2 show that ten jerature has little effect on the selectivity as the cis trans ratio remains constant at 4-5 1, but the reaction rate as expected increased (from 108 to 259 mol/hr/gm cat.). 

Table 2 Effect of temperature on activity and selectivity with 5% Rh/C in decane solvent at 10 bar. 

PRZ/WIS] Przepiera, A., Wisniewski, M., Dabrowski, W., Jablonski, M., Enthalpy of solution and effect of temperature on activity coefficients in the MSO4-H2SO4-H2O system, J. Therm. Anal, 50, (1993), 1139-1143. Cited on pages 191, 425, 426. 

Comparison of these constants with those of the previous example will illustrate again the effect of temperature on activity coefficients. 

Organic Pollutants in Water Using DSA Electrodes, In-Cell Mediated (via Active Chlorine) Electrochemical Oxidation, Fig. 6 Effect of temperature on active chlorine concentration. Conditions i = 20 mA cm -",pH 5.5, initial concentration of chloride 0.1 M... 

Effect of temperature on activity of FP-cellulase (FPA 1), endoglucanase (CMCA 2) and aryl-B-glucosidase (3GA 3) of A. terreus ATG5. 

Pig. 1.13 Effect of temperature on activity l-Fei xO based catalysts 2-Fe304-CoO based catalysts 3-Fe304 based catalysts (p = 15 MPa Sv = 3 X lO h-l). 

The most convenient and comparable measurement of enzyme stabUity is the half-life at a given temperature (other incubation conditions being defined), i.e. the time period over which half the initial activity of an enzyme is lost. Additional information on the effect of temperature on activity can be important, for instance the shape of a plot of logio of percent activity remaining versus time of incubation can indicate whether irreversible thermal denaturation is the sole eause of loss of activity or whether additional factors are involved, such as autolysis, renaturation, or substrate effects. 

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