Magnitudes of entropy changes

The typical magnitudes of entropy changes in chemistry are such that they are generally reported in J mol" K" instead of kJ mol" K". ... 

Even if one of the processes is not chemical but is categorized as a phase change, for example, evaporation, the extended De Donder s equation (Equation 13.17), is known to be valid. Any large magnitude of entropy production rate (diS/dt) due to evaporation might give a correlation such as... 

The limited available data suggest that solvent has relatively small effect on the fragmentation rate, although the change in solvent may affect the relative magnitudes of entropy and enthalpy of activation [102], For those reasons the... 

Table III presents integral excess entropies of formation for some solid and liquid solutions obtained by means of equilibrium techniques. Except for the alloys marked by a letter b, the excess entropy can be taken as a measure of the effect of the change of the vibrational spectrum in the formation of the solution. The entropy change associated with the electrons, although a real effect as shown by Rayne s54 measurements of the electronic specific heat of a-brasses, is too small to be of importance in these numbers. Attention is directed to the very appreciable magnitude of the vibrational entropy contribution in many of these alloys, and to the fact that whether the alloy is solid or liquid is not of primary importance. It is difficult to relate even the sign of the excess entropy to the properties of the individual constituents.

With motion along the connodal curve towards the plait point the magnitudes Ui and U2, Si and S2, and ri and r2, approach limits which may be called the energy, entropy, and volume in the critical state. The temperature and pressure similarly tend to limits which may be called the critical temperature and the critical pressure. Hence, in evaporation, the change of volume, the change of. entropy, the external work, and the heat of evaporation per unit mass, all tend to zero as the system approaches the critical state ... 

Use data in Table 7.3 or Appendix 2A to calculate the standard entropy change for each of the following reactions at 25°C. For each reaction, interpret the sign and magnitude of the reaction entropy, (a) The synthesis of carbon disulfide from natural gas (methane) CH4(g) + 4 S(s, rhombic) - CS2(1) +... 

A Hsys — < sys (constant P) Remember also that the heat flow for a system is always equal in magnitude but opposite in sign to the heat flow of the surroundings sys = - surr S o A H s = < surr Furthermore, we have already required constant temperature, so the heat flow of the surroundings measures the entropy change of <75 c,... 

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