Melting point free energy change

Further information on the effect of polymer structure on melting points has been obtained by considering the heats and entropies of fusion. The relationship between free energy change AF with change in heat content A// and entropy change A5 at constant temperature is given by the equation... 

Let us first consider the liquid-solid phase transformation. At the melting point (or more appropriately, fusion point for a solidification process), liquid and solid are in equilibrium with each other. At equilibrium, we know that the free energy change for the liquid-solid transition must be zero. We can modify Eq. (2.11) for this situation... 

Figure 5.2.2 Plot of Gibbs free energy changes of the thermal reduction (green line) (Fe3(>4 = 3 FeO + 1/2 O2), FeO oxidation (red line) (3 FeO + CO2 = Fe3C>4 + CO), and overall reaction (blue line) (CO2 = CO + 1/2 O2) for the iron-oxide-based cycle. The vertical lines show the melting points of the indicated iron-oxide phases.

The ideal solubility pertains to the effect of the crystalline structure on solubility. A solute molecule must first dissociate from this crystal lattice before it can go into solution. This dissociation from the crystalline lattice is accompanied by a free energy change. The more energy it takes to free a solute molecule from its crystal (i.e., the higher the melting point), the lower the solubility. 

Useful generalizations of factors affecting Tm can be derived from the application of macroscopic thermodynamics. At Tm, the free energy change is zero, i.e., AG, = Mlm - TmA.S,n - 0, whence T i = AHmItsSm- Thus a high melting point ... 

Consider the crystallization of a melt with a freezing point T, . At the free-energy change per mole associated with the solid-to-liquid... 

As illustrated by the crossover point of the curves in Fig. 10. lb, the isobaric free energy change of the polymer bulk system at the melting point appears as... 

Gibbs free-energy change when 1 mole of a compound is synthesized from its elements in their standard states. (8.4) standard melting point. The melting point of a substance at 1 bar pressure. (5.2) standard molar enthalpy of formation (Aff J). The enthalpy change that results when 1 mole of a compound in its standard state is formed from its elements in their standard states. 

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