Entropy Change in Process

Entropy change of an ideal gas is derived from the thermod5mamic relations (Equation 3.42a or 3.42b) and expressed as 

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Sturtevant JM (1977) Heat capacity and entropy changes in processes involving proteins. Proc Natl Acad Sci U S A 74(6) 2236... 

Definition of Entropy Judging Entropy Changes in Processes... 

Sturtevant, J. M. "Heat Capacity and Entropy Changes in Processes Involving Proteins." Proc. Natl. Acad. Sci, USA, 74,2236-2240 (1977). 

The Caratheodory analysis has shown that a fundamental aspect of the Second Law is that the allowed entropy changes in irreversible adiabatic processes can occur in only one direction. Whether the allowed direction is increasing or decreasing turns out to be inherent in the conventions we adopt for heat and temperature as we will now show. 

E3.7 A block of copper weighing 50 g is placed in 100 g of HiO for a short time. The copper is then removed from the liquid, with no adhering drops of water, and separated from it adiabatically. Temperature equilibrium is then established in both the copper and water. The entire process is carried out adiabatically at constant pressure. The initial temperature of the copper was 373 K and that of the water was 298 K. The final temperature of the copper block was 323 K. Consider the water and the block of copper as an isolated system and assume that the only transfer of heat was between the copper and the water. The specific heat of copper at constant pressure is 0.389 JK. g l and that of water is 4.18 J-K 1-g 1. Calculate the entropy change in the isolated system. 

The following pictures show a molecular visualization of a system undergoing a spontaneous change. Account for the spontaneity of the process in terms of the entropy changes in the system and the surroundings. 

In thermodynamics, entropy enjoys the status as an infallible criterion of spontaneity. The concept of entropy could be used to determine whether or not a given process would take place spontaneously. It has been found that in a natural or spontaneous process there would be an increase in the entropy of the system. This is the most general criterion of spontaneity that thermodynamics offers however, to use this concept one must consider the entropy change in a process under the condition of constant volume and internal energy. Though infallible, entropy is thus not a very convenient criterion. There have, therefore, been attempts to find more suitable thermodynamic functions that would be of greater practical... 

If the system is neither closed nor thermally insulated, then the change in the entropy with time consists of two quantities of the time change in the entropy as a result of processes occurring within the system S and of entropy changes in the surroundings, caused by transfer of the entropy from the system in the reversible process Sc... 

Fiolitakis, E., Some Aspects on the Entropy Change in Onsa-ger s Sense for Irreversible Chemical Processes, to be published... 

The second important solvent effect on Lewis acid-Lewis base equilibria concerns the interactions with the Lewis base. Since water is also a good electron-pair acceptor129, Lewis-type interactions are competitive. This often seriously hampers the efficiency of Lewis acid catalysis in water. Thirdly, the intermolecular association of a solvent affects the Lewis acid-base equilibrium242. Upon complexation, one or more solvent molecules that were initially coordinated to the Lewis acid or the Lewis base are liberated into the bulk liquid phase, which is an entropically favourable process. This effect is more pronounced in aprotic than in protic solvents which usually have higher cohesive energy densities. The unfavourable entropy changes in protic solvents are somewhat counterbalanced by the formation of new hydrogen bonds in the bulk liquid. 

ENTROPY CHANGES IN REVERSIBLE PROCESSES 131 For the specific case of the expansion of an ideal gas, because AU=0,... 

To determine the entropy change in this irreversible adiabatic process, it is necessary to find a reversible path from a to b. An infinite number of reversible paths are possible, and two are illustrated by the dashed lines in Figure 6.7. 

Then from the entropy change in a reversible, isothermal process [Equation (6.72)]... 

While the first law allows us to calculate the energy change associated with a given process, it says nothing about whether or not the process itself will take place spontaneously. This is the province of the second law of thermodynamics and leads to the introduction of another state function, entropy, S. The entropy change in a system which moves from state 1 to state 2 is defined by... 

The entropy change in a process is given by eqn. (14) and it follows that entropies can be assigned to individual substances. As entropy is a state function, its value will depend on the state of the substance and, with the aid of eqn. (14), the entropy difference between any two states can be calculated. The third law enables a zero to be fixed for the entropy scale and there are tables [5—9] which give the entropies of many substances in their standard states at the reference temperature of 298 K. As long as there is no change of phase, the entropy at any other temperature can be calculated using... 

Shown that entropy change in a binary mixture for isothermal process is maximum when Xj=X2... 

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