Reversible melting

Compute the entropy change when 1.00 g of ice is melted reversibly at 0°C, and when 1.00 g of liquid water is reversibly evaporated at 100°C. 

It is possible to classify polymers by their structure as linear, branched, cross-linked, and network polymers. In some polymers, called homopolymers, merely one monomer (a) is used for the formation of the chains, while in others two or more diverse monomers (a,p,y,...) can be combined to get different structures forming copolymers of linear, branched, cross-linked, and network polymeric molecular structures. Besides, on the basis of their properties, polymers are categorized as thermoplastics, elastomers, and thermosets. Thermoplastics are the majority of the polymers in use. They are linear or branched polymers characterized by the fact that they soften or melt, reversibly, when heated. Elastomers are cross-linked polymers that are highly elastic, that is, they can be lengthened or compressed to a considerable extent reversibly. Finally, thermosets are network polymers that are normally rigid and when heated do not soften or melt reversibly. 

As a part of his classic study of reactive free radicals in the early 1930s, Paneth observed that methyl radicals react with a heated antimony mirror to produce tetramethyldistibine (22) (27). This distibine has quite remarkable properties. It forms intensely colored red crystals which melt reversibly to a yellow oil. Similarly, solutions of tetramethyldistibine are pale yellow. Although these color changes are clearly due to changes in phase rather than strictly temperature, they have been termed thermochromic... 

Pure TcOFs melts reversibly and without decomposition at 57-58 °C. The volatile orange solid is deep red-orange in the liquid state [86]. According to F NMR, Tc NMR, Raman and IR spectroscopy, the structure of the TcOFs molecule is pseudo-octahedral. The vibrational frequencies are presented in Table 10.11.A. 

Consider a system consisting of an ice cube, (a) Under what conditions can the ice cube melt reversibly (b) If the ice cube melts reversibly, is A zero for the process Explain. 

In general cyclopropenones are stable compounds which melt reversibly but decompose on stronger heating. However 2,3-dichloro-cyclopropenone as a neat liquid decomposes readily at room temperature, sometimes explosively [93]. In dilute solutions in methylene chloride at room temperature it has a half-life of only a few hours the product is thought to be a spiran [93] ... 

Polymer cold cryst. hot cryst. conformational Cp RAF C) reversible melting reversing melting... 

The Ge(lll)-(2xl) cleavage structure undergoes a similar activated transition at 100 °C to a c(2 X 8) structure. At 300 C, the c(2 x 8) experiences a reversible first-order phase transition to a (1x1) structure currently regarded as a premelting transition [48]. Finally, at 785 °C, the (1 x 1) surface layer melts reversibly [49-51] before the bulk crystal melts at 937 °C. 

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