Reactant Melting and Decomposition Enthalpy

Silver and Cadmium Nitrates Studies of the decomposition rates for solid and liquid (melted) reactants are of the top most importance for verification of the CDV mechanism. Measurements of such kind have been recently described by L vov and Ugolkov [11] for the decompositions of the anhydrous nitrates of silver and cadmium. Melting temperatures for these salts are equal to 483 and 633 K, respectively. The final results of these experiments (with an allowance for some corrections mentioned in Sect. 16.11) are presented in Table8.3. 

As can be seen from Table 8.3, regardless of the difference in temperatures, the decomposition rates for AgN03 and Cd(N03)2 in the solid and molten states appear to be about the same. (With a temperature difference of 100 K, a rate increase by 2-3 orders of magnitude could be expected.) For some reason the decompositions of the solid reactants slow down after their melting. The magnitude of the molar enthalpy (parameter E) rises by about 20 kJ mol  

As will be shown in Sect. 16.11, the experimental results for both nitrates agree with the theoretical calculations. 

Calcium Nitrate The results of similar experiments for Ca(N03)2 by Ettarh and Galwey [13] are also in a full agreement with the above approach. The melting point for Ca(N03)2 is 836K. The E parameters measured in [13] for solid (774-820K) and melted nitrate (229 10 and 315 20kJ moP ), 

the decelerating influence of melting on the rate of reactant decomposition is in complete agreement with the CDV mechanism. It is doubtful that any other explanation of this unusual effect can be found within the framework of commonly accepted views. 

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