Heats of transformation

Note These data have been obtained from die complete tirermodynamic data tabulated in Kubaschewski et al. (loc. cit.), with the approximation of tire simple two-term equation. This should serve for calculations not requiring an accuracy of better than 2kJmoG 02, which is normally the case for industrial applications. Solid state ctystal transformations which usually only have relatively small heats of transformation, have been ignored. 

AH = latent heat of transformation = equilibrium temperature (absolute). 

These techniques help in providing the following information specific heat, enthalpy changes, heat of transformation, crystallinity, melting behavior, evaporation, sublimation, glass transition, thermal decomposition, depolymerization, thermal stability, content analysis, chemical reactions/polymerization linear expansion, coefficient, and Young s modulus, etc. 

Eutectic arrest In a cooling (or heating) curve an approximately exothermal segment corresponding to the time interval during which the heat of transformation from the liquid phase of two or more conjugate solid phases is being evolved (or conversely). 

There are two heat factors involved in cUiy phase change. They are "heat capacity", i.e.- Cp or Cy, and "heat of transformation", usually denoted as H. 

Reiterating, heat of transformation, or H, is involved in change of form of the material while heat capacity relates to its internal change in temperature as it approaches another point of change. Both of these constants are based upon the standard of energy, or heat, of one (1.00) calorie. Heat capacity is also known as thermal capacity. 

L, or G refer to either soUd, liquid or gas. Note that this internal energy differs from the heat of transformation, H. (This concept is perhaps one of the more difficult ones for one to grasp. However, the internal energy is that energy the substance has at a given temperature). Thus, the relation between Hs,l,g and Cp is ... 

Note that AH here is a heat of transformation involved in a change of state whereas AHs,l,g refers to change in internal heat for a given state of... 

The heat of transformation is defined as the change in enthalpy that results when one mole of a substance undergoes a specific change of state such as melting, evaporation, or allotropic modification. 

Table 2. Heat of Transformation of Various Forms of Si02a,b...

The latent heat ol fusion of sodium hydroxide per gram is 400 cals. potassium hydroxide, 28-6 cals. rubidium hydroxide, 15 8 cals. and csesium hydroxide, 107 cals. The corresponding values in calories per mol. are 1602, 1606, 1614, and 1609 cals, respectively. The heat of transformation of sodium hydroxide per gram is 24 7 cals. potassium hydroxide, 27T cals. rubidium hydroxide, 16 8 cals. and csesium hydroxide, 11 8 cals. The corresponding values in calories per mol. are 990,1522,1702, and 1763 cals, respectively. 

The identity of the II and V modification does not here involve the vanishing of the sums of the heats of transformation Q3JrQi- -Q3=6, for this could occur only if... 

S (c, monoclinic). The heat of transformation of monoclinic to rhombic sulfur was measured by Bronsted,3 Mitscherlich,2 Tammann,2, 3 Lewis and Randall,1 Wigand,1 and Mondain-Monval.1, 4 Using Lewis and Randall s5 values for the heat capacities, we have found that Bron-sted s3 data yield, for the transformation, T=0.120— 0.0005 (i+273.1) -0.00000125 (t+273.1)2 whence, at 18°, T= -0.080, and at 95°, the normal transition temperature, T=—0.088. Mondain-Monval1,4 found T= —0.087. 

Hence, the heat of transforming the labile variation into the stable one is 28 cal/g. 

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