Temperature-dependence of enthalpy

Standard heat data are usually compiled at 298 K, and to calculate the heat of reaction at an arbitrary temperature, the temperature dependency of enthalpies of reaction species have to be considered. These are generally dependent on temperature as follows... 

Figure 6AO Temperature dependence of enthalpy (A) and heat capacity (B) for CaMg-Si206 component in crystalline, vitreous, and molten states at various T conditions. Reprinted with permission from Richet and Bottinga (1986), Review of Geophysics and Space Physics, 24, 1-25, copyright 1986 by the American Geophysical Union.

Fig. I. Example of the temperature dependence of enthalpy relative to 25°C. Hi - Hyth is- anJ heal capacity. Cp. The data arc tor fluorite, CaF K K Kelly. 191)0). The discontinuities in the lines correspond In the a to p transition 11424 K> and the fusion 11691 K)...

It is tempting to suppose that all the denaturation enthalpy at Tx is provided by the disruption of nonpolar contacts, i.e., actually by van der Waals interactions, but that the temperature dependence of enthalpy is determined by hydration of nonpolar groups. The latter is supported by the correlation found between AnCp and the saturation of the native structure by the contacts between the nonpolar groups (Table I). However, this simple model immediately raises two questions Why do proteins with different concentrations of nonpolar contacts have the same denaturation enthalpy values at Tx Is it reasonable to neglect the contribution of hydrogen bonds in the denaturation enthalpy ... 

The large dependence of enthalpy with temperature is indicative of a specihc interaction, even though that the affinities of these monomeric interactions between TRAF2 and receptors are rather low. As suggested from thermodynamic studies of protein-DNA interactions, a non-specific weak complex held together by electrostatic forces often exhibits little temperature dependence of enthalpy (Ladbury, 1995). 

To calculate an approximate value of [M]e, consider the monomer and the polymer in their standard states and assume that there is no significant temperature dependence of enthalpy or entropy of polymerization so that the and A5° data of Table 6.13 can be used. For = 373 °K, Eq. (6.198) then yields. 

The temperature dependencies of enthalpy, free enthalpy, entropy, and heat capacity of glasses and crystals are schematically indicated in the three drawings at the bottom of Fig. 2.116 (see also Fig. 2.23). Enthalpy, entropy, and heat capacity increase with temperature, while the free enthalpy decreases. The reasons for the trends of these functions with temperature can be derived from a detailed understanding of heat capacity (see Sects. 2.3). The link between heat capacity and enthalpy is obvious from its definition (Fig. 2.10). Entropy is similarly related to heat capacity in Fig. 2.19 (see also Fig. 2.22). The free enthalpy is then fixed by G = H - TS. 

Figure 5.4 Temperature dependence of enthalpy, free energy, and T entropy.

Heat capacity expresses the temperature dependency of enthalpy. 

Temperature Dependence of Enthalpy, Gibbs Energy, Entropy and Heat Capacity of Solids... 

Figure 3.29. Schematic outline of the temperature dependence of enthalpy Hx is calculated by adding Cp multiplied by the temperature increase to the standard enthalpy // gg at 298.15 K.

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