Thermodynamics heat capacities

The treatment of heat capacity in physical chemistry provides an excellent and familiar example of the relationship between pure and statistical thermodynamics. Heat capacity is defined experimentally and is measured by determining the heat required to change the temperature of a sample in, say,... 

Instrumental methods in chemistry make it possible to characterize any chemical compound by a very large number of different kind of measurements. Such data can be called observables. Examples are provided by Spectroscopy (absorbtions in IR, NMR, UV, ESCA. ..) chromatography (retentions in TLC, HPLC, GLC. ..) thermodynamics (heat capacity, standard Gibbs energy of formation, heat of vaporization. ..) physical propery measures (refractive index, boiling point, dielectric constant, dipole moment, solubility. ..) chemical properties (protolytic constants, ionzation potential, lipophilicity (log P)...) structural data (bond lengths, bond angles, van der Waals radii...) empirical structural parameters (Es, [Pg.34]

Cy The thermodynamic heat capacity of the clusters in units of energy/K. 

Now only the first term on the right hand side is the thermodynamic heat capacity. The second term is a kinetic contribution that will only vanish if the system is at equilibrium (i.e., independent of time). But this can never happen when the DSC is operating in the scanning mode. Furthermore, since the kinetic term is inversely proportional to the scanning rate, dT/dt, the error in assuming that dH/dT is the true heat capacity, increases as the scanning rate is reduced Why, then, has the DSC yielded such excellent results in comparison with the adiabatic calorimeter ... 

Now the first term is the kinetic term that is desired and the second term, which contains the thermodynamic heat capacity, must vanish since dT/dt = 0. Thus, at first sight, it would appear that the DSC, operating in the isothermal mode provides an excellent, convenient, and unequivocal means of measuring the kinetics of the approach of a sample to equilibrium under constant thermodynamic conditions. However, let us examine more carefully how a specimen is maintained at a constant temperature in a DSC. Using the same procedure of expanding the total derivative in partials we have ... 

Treating dHIdT as an apparent heat capacity Cp, equation 10 allows the separation of the latent heat contribution from the thermodynamic heat capacity if Cp,c and Cp a, the crystalline and amorphous heat capacities, are known (as well as the temperature-dependence of the heat of fusion, AH(). 

Since dH/dT = Cp is the true thermodynamic heat capacity at equilibrium, accounts for it and all the other possible contributions caused by the nonequilibrium state of the system (or by the changes in its properties). For this reason is also the apparent specific heat, that is, app. Figure 16 shows Cp pp... 

As described in Section 2.2, the heat capacity indicates how much heat is needed to raise the temperature of 1 g of the sample by 1 °C. In equilibrium thermodynamics heat capacity is a function of state. Two major heat capacity variants are in use ... 

Figure 2.119. Separation of a scan of PET into the nonreversing component or IsoK baseline and the reversing or Thermodynamic heat capacity from an SSDSC experiment from the raw data labeled above. Upper curve shows the reversing heat capacity component bottom curve, is the IsoK baseline. An insert of the cold crystallization process demonstrates the temperature steps with the resultant modulated effect on the heat flow with its associated IsoK baseline. [From Ye (2006) courtesy of Perkin-Elmer.l...

The most important contribution of statistical thermodynamics to chemistry is in providing models for molecular structure. As an example let us consider the observation that heat capacity of graphite is higher than that of diamond at ambient temperature. Classical thermodynamics cannot give an explanation for this observation, since it is energy-entropy transformation theory without reference to material composition. According to statistical thermodynamics, heat capacity depends on the frequency of oscillations of the atoms around their equilibrium... 

Heat Calorimetry Reaction, adsorption, absorption, hydration, mixing, formation, catalysis, thermodynamics, heat capacity, kinetics,... 

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