Effect of temperature on stability

A convenient, approximate method which is useful for estimation of decomposition rates at room temperature makes use of the ratio of rate constants at room temperature (Tj) and at a higher temperature T2). If we subtract the Arrhenius equations at temperatures Tj and T2, assuming that the log A term is the same at each temperature, we obtain 

We must, of course, have a value of in order to be able to use these equations for the calculation of the room temperature rate constant ky If we only require a rough estimation of kj then we can assume a mid-range value of E, say 75 kj mol, for these calculations. 

The first-order rate constant for the hydrolysis of sulfacetamide at 120°C is 9 x 10 s and the activation energy is 94 kJ mol. Calculate the rate constant at 25°C. 

The required value of k can be interpolated from this plot at room temperature, and the activation energy E can be calculated from the gradient, which is -E /2.303R. Values of E are usually within the range 50-96 kJ mol.  

An alternative method of data treatment is to plot the logarithm of the half-life tgj as a function of reciprocal temperature. From equation (4.13), fg 5 = 0.693/k. Therefore, 

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Figure 10. Effect of temperature on stability of nickel in presence of H2S and H2. Data from References 34 and 35.

Fig. 3. Effect of temperature on stability of soluble invertase ( ) and Dowex-lx4-200/invertase complex (O).

Livesey, J., Awang, D., Amason, J., Letchamo, W., Barrett, M., and Pennyroyal, G. 1999. Effect of temperature on stability of marker constituents in Echinacea purpurea root formulations. 

TABLE 40.4 Effect of Temperature on Stability Constants (Kj.) of Inclusion Complexes of Ethyl 4-Biphenylylacetate with Various (3-CyDs, and Their Thermodynamic Parameters in Water... 

Table 38.4 Effect of temperature on stability constants (KJ of inclusion complexes of ethyl 4-biphenylylacetate with various -CyDs, and their thermodynamic parameters in water...

Figure 1. Effect of temperature on stability and activity of Clostridium thermohydrosulfUriciun strain 39E amylopuUulanase. (a) TherW stability. The enzyme was placed in acetate buffer (SO mM, pH 6.0) with 5 mM CaC and preincubated at various temperatures for 30 min, and then residual amylopuUulanase activities were assayed, (b) Effect of heat on activi. The enzyme activity was assayed at various temperatures by the standard assay method (30 min incubation). (Reproduced with permission from Ref. 55. Copyright 1988, The Biochemical Society and Pordand Press, London.)...

Fig. 3.2.7 Left panel Effects of temperature on the luminescence intensity and stability of the protein P from Meganyctiphanes. The initial light intensity was measured with F plus P in 5 ml of 20 mM Tris-HCl/0.15 M NaCl, pH 7.5, at various temperatures. In the stability test, P was kept at the indicated temperature for 10 min, then mixed with 5 ml of 25 mM Tris-HCl/1 M NaCl, pH 7.59, containing F, to measure initial light intensity. Right panel Effect of the concentration of salts on the light intensity of the luminescence of F plus P, in 25 mM Tris-HCl, pH 7.6, at near 0°C. In the case of NaCl, the light intensity decreased to about a half after 10 min. From Shi-momura and Johnson, 1967, with permission from the American Chemical Society.

Because of the opposite effects of temperature on the stability of CO and CH4, the odd result is that, as the temperature increases, graphite deposition is less likely for starting mixtures which are near stoichiometric, but it is more difficult to produce pure methane by removing water and allowing the mixture to react further. Because of equilibrium considerations, the final approach to pure methane must be done at a relatively low temperature. 

With DMA the effect of temperature on the modulus can be studied. By increasing the temperature from -150 to 300°C, one encounters several transitions in PA (Fig. 3.1). There is a transition at about —120°C, the y-transition, which is due to the mobilization of methylene units. There is also a transition at —30°C, which is present in wetted aliphatic PA this is due to non-H-bonded amide units and is termed the /J-transition. At about 50°C the glass Uansition (Tg) (a-transition) of the aliphatic polyamides PA-6 and PA-6,6 occurs. At this Uansition, the modulus is lowered considerably. For partially aromatic PA, the Tg occurs above 100°C. The last transition is the flow temperature, at which temperature the material melts the flow temperature and the melt temperature, as measured by DSC, correspond well. The modulus is a measure of dimensional stability and increases with crystallinity and filler content (Fig. 3.12). 

The effects of temperature on carotenoid content can be considered from three perspectives (1) evaluation of stability or retention of carotenoids, (2) study of the chemical changes (isomerization, oxidation, epoxy-furanoid rearrangement), and (3) their effects on the nutritional value and other carotenoid actions in humans. The first two topics are discussed in the following sections. The third is presented in Section 3.2.4.1 of Section 3.2. 

Temperature variation may also be a relevant factor in flowrate stability. Since the viscosity of the solvent is temperature dependent, wide swings in the ambient temperature can directly affect pump performance. The direct effects of temperature on pump performance usually are far smaller, however, than the effects on retention and selectivity therefore, control of column temperature is generally sufficient to obtain high reproducibility. 

Li, J. and Carr, P.W., Effect of temperature on the thermodynamic properties, kinetic performance, and stability of polybutadiene-coated zirconia, Anal. Chem., 69(5), 837, 1997. 

Figure 2.7 Effect of various factors on nanoparticle dispersion (as determined by tracking the absorbance oTIspr) as a function of applied C02 pressure, (a) effect of temperature on DDT-stabilized gold nanoparticles dispersed in hexane (b) effect of solvent on DDT-stabilized gold nanoparticles at room temperature (c) effect of ligand on gold...

This is very useful for generating modulus versus temperature data on rubber compounds. The effects of temperature on this important material property can be obtained over a wide temperature range (typically -150 to +200 °C), along with the glass transition temperature and information on thermal stability. 

Silica from zeolite migrates less readily. In the magnesia-alumina system, spinel, as identified by X-ray diffraction, is inactive for SO2 removal. The effect of temperature on steam stability, oxidative adsorption and reductive desorption of SO2 are described. Five commercial catalyst types are ranked for SOx removal. 

Abstract—The equilibrium diagrams of the binary systems of sulphuric add with nitromethane and with o-y m- and p-nitrotoluene have been investigated. It has been shown that addition compounds of the type 1 1 are formed in these systems, analogous to the compound sulphuric acid-nitrobenzene (Chebbuuez Helv, Chim, Acta 1923 6 281 and Masson J. Chem. Soc. 1931 3201)t The formation of these addition compounds is due to hydrogen bonding between the components, rather than to proton transfer. Their stability in the crystalline phase seems to be contradictory to the known basicities of mononitrocompounds (Gillespie and Solomons J. Chem. Soc, 1957 1796), because of the effect of temperature on the equilibria in the liquid phase. 

A detailed study of the effect of temperature on the reaction kinetics of etr with a set of acceptors over a broad time interval of 10 5-l s in the region of ultralow temperatures (4.2-100 K) was performed in ref. 79. For the acceptors CrO, Fe(CN)jF, and N02, the decay curves for electrons et stabilized in deep traps of a water-alkaline (8M NaOH) matrix were found to vary only slightly with variation of temperature. The same result was obtained for the reactions of these acceptors with e stabilized in deep traps of vitrified mixtures of water with ethylene glycol [105]. Thus, at temperatures of 4-100 K, the main contribution of the reaction of et with the above acceptors in both matrices is made by a temperature-independent channel of electron tunneling. 

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