Calcium free energy change

The standard free energy changes for these reactions also are given in Figure 4.15. While the free energy for the second step (calcium reduction) is negative at all temperatures (as... 

One of the important differences between calciothermic and aluminothermic reduction of oxides concerns the interaction between the reduced metal and the reductant. Calcium does not form stable solid solutions or alloys with the reduced metals calcium contamination in the metal is, therefore, relatively small. Aluminum, on the other hand, readily forms solid solutions with the reduced metals, and the product generally contains appreciable quantities of residual aluminum. This is not a serious problem because in many cases either a certain aluminum content is desired in the reduced metal or the residual aluminum can be effectively removed in post-reduction purification operations. The extent of the contamination of a reduced metal with the reductant can be related to factors such as the reaction temperature, the standard free energy change associated with the reaction, and the slag composition. Let the following generalized reaction be considered ... 

If the free energy changes for the reduction of the sulfate to make H2S rather than SO2 had been considered in this analysis, the oxides of several more elements would have been included in the boxed-off area of appropriate materials. From past practice, however, it is known that oxides of calcium, strontium and lithium, for instance, are not as effective. An appropriate future area of research would be to investigate those materials more thoroughly. 

Now.let us use this information to determine the free energy change associated with the reaction in which calcite dissolves in acid, to form the calcium and bicarbonate ions. 

Calcium carbonate is insoluble in water. Yef it dissolves in an acidic solution. Calculate the standard enthalpy, entropy, and Gibbs free energy change for the reaction between sohd calcium carbonate and hydrochloric acid. What drives the reaction, the enthalpy change, or the entropy change ... 

Measurements of the steady state phosphoprotein level at different temperatures revealed that phosphoprotein formation is accompanied by a large and constant enthalpy change of 48 kJ/mol. In contrast, the likewise quite high activation energy of phosphoprotein formation exhibits a pronounced break between 20°C and 30°C. A break in the Arrhenius plot of the calcium-dependent ATPase has been observed in the same temperature range and has been interpreted as transitions between two activity states of the enzyme. Apparently, the phosphorylation of the calcium free protein by inorganic phosphate exhibits a similar kind of activity transition as observed for the calcium-dependent interaction of the transport protein with ATP131. A similar transition phenomenon complicates the time course of phosphoprotein formation... 

The free energy required to overcome the transition barrier for this step is 18 and 22 kcal/mol with respect to 1NT2 for Models A and B in gas-phase respectively (Table 2). There is not much change in this barrier ( 1 kcal/mol) even in the presence of protein environment and water for Model B. Water molecules W362 and W615 maintain their coordination with calcium, and ASP303 and calcium respectively throughout this proposed reaction path until the formation of the final product (Fig. 5). 

The second category of aqua ions corresponds to a mixture of differing N values (and symmetries) with almost the same free energy, readily modified by changing salt concentration, temperature (and perhaps even hydrostatic pressure). The rather indifferent choice between N = 7, 8, 9 and 10 may be characteristic for calcium(II), the rare earths and probably also for thorium(IV). The third category are cations with so large radii and so low positive charge (probably K+, Rb+, Cs+ and Ba+2, perhaps even Tl+) that the nearest water molecules are so relatively weakly perturbed and oriented by the cation that the situation is similar to the second layer of water molecules around Co(NH3) 3 or Cr(OH2)g 3, or even N(CH3)4. ... 

Chibowski, E., Holysz, L., and Wojcik, W, Changes in zeta potential and surface free energy of calcium carbonate due to exposure to radiofrequency electric field, Colloids Surf. A, 92, 79, 1994. 

The effect of s—d hybridization on the relative stability of the structures of metallic Ca and Sr has been studied as a function of temperature and pressure within the context of the pseudopotential theory for metals. The inclusion of hybridization is found to favour the f.c.c. structure at all pressures and, in particular, is necessary to explain the observed f.c.c. structure in these metals at zero temperature and pressure. Phase boundaries are calculated by equating the free energy of the f.c.c. structure to that of the b.c.c. structure. Temperature-induced phase transitions are predicted to occur at 555 K in Ca and 625 K in Sr as compared with the actual temperatures of 721 and 830 K. From the changes in free energy of the reactions of the alkaline-earth metals with gases as a function of temperature, it is confirmed that at 298— 1400 K almost all of the residual gases in electrovacuum devices combine with the metals to form stable compounds. The dehydration of calcium... 

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