The heat capacity peak

Ai/ ai and Ai/y.H. should be identical if the transition proceeds as a two-state reaction. The latter quantity is the so-called van t Hoff enthalpy and represents the standard enthalpy change of a one-step reaction. For a reaction of the type N nD the van t Hoff enthalpy can be approximately calculated by 

Since the van t Hoff enthalpy is a mecisure of the sharpness of the peak, any flattening of the heat capacity curve, associated e.g. with sequential 

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Figure 4.13 shows the heat capacity of NiCE as a function of temperature.12 The heat capacity peak at 52 K occurs at the Neel point. Below this temperature, NiCl2 becomes antiferromagnetic and the electron spins become increasingly ordered, so that at 0 Kelvin, So = 0. Busey and Giauque13 were able... 

The heat capacity peak, characteristic of the transition, reflects the excess heat capacity arising from the enhanced enthalpy fluctuations that occur in the temperature range of the transition. In the case of a two-state transition, the thermodynamic functions are obtained in a straightforward way from the area QD under the peak (corrected for the baseline), which measures the overall enthalpy change resulting from the transition, and the overall heat capacity difference (ACp) ... 

The heat capacity peaks obtained by adiabatic calorimetry [156] using Grafoil GTA show maxima at slightly lower temperatures in the submonolayer regime at about 27.5 0.1 K from 0.169 up to 1.000 monolayers. A vdue of 28.7 K was reported beyond the complete monolayer at a coverage... 

Figure 58. Normalized maximum of the heat capacity peaks of CO on graphite foam at the head-tail critical temperature = 5.18 K as a function of the monolayer coverage. (From Ref. 381.)...

It is desirable to have direct evidence from other experimental methods such as neutron diffraction and scattering. The dielectric constant of the hydrogen sulphide clathrate increased as the temperature decreased down to 10 - 15 K [13]. It decreased at the lower temperature. The temperature of the maximum of the dielectric constant depended on the occupancy x. However, it was always higher than the temperature of the heat capacity peak. The mechanism of the phase transition at 7.6 K will be discussed below. 

Figure 8. Temperature dependence of heat capacity near the SmA-SmB, phase transition of 3(10)OBC. The data were obtained from 2- (a), 3- (b), 4- (c), 5- (d), 6- (e) and 7-layer (0 films. Both layer-by-layer transition and sharpness of the heat capacity peaks are clearly shown.

When pressure is applied to the /S-phase crystal, it is found that the ferromagnetic transition temperature decreases [37-39]. As shown in Figure 15.27(a)-(f), the transition temperature as defined by the heat capacity peak decreases by about 40% as the pressure is increased up to 770 MPa. This means that the... 

Figure 3. Illustration of the determination of the calorimetric enthalpy A//cai by integration of the heat capacity peak. The error of taking a linear bas(v line for integration (dotted) instead of the sigmoidal curve is in most cases negligible. Positive and negative errors in the area compensate each other. The parameters used in the calculations (equation 44) are given in Figure 1.

Cp n T) is the heat capacity function of the native state, ACp T) = Cp j) T)-Cp n(T) is the difference between the extrapolated heat capacity functions of the denatured and native states at temperature T, and the term ACpOiD describes the sigmoidal baseline under the transition peak. The term [A°/f°(T)] aDQ N characterises the heat absorption peak. The product Q n d = ctN(l Q n) is responsible for the appearance of the characteristic shape of the heat capacity peak. Typical curves are given in Figures 1 and 4. 

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