Thermodynamics

348 | ThermodynamicsW shHOT BODY80°C(Entropydecreases)HeatGASFIGURE 7–24The paddle-wheel work done on a gasincreases the level of disorder(entropy) of the gas, and thus energy isdegraded during this process.COLD BODY20°C(Entropyincreases)FIGURE 7–25During a heat transfer process, the netentropy increases. (The increase in theentropy of the cold body more thanoffsets the decrease in the entropy ofthe hot body.)FIGURE 7–26The use of entropy (disorganization,uncertainty) is not limited tothermodynamics.© Reprinted with permission of King FeaturesSyndicate.Tis converted to the internal energy of the gas, as evidenced by a rise in gastemperature, creating a higher level of molecular disorder in the container.This process is quite different from raising a weight since the organizedpaddle-wheel energy is now converted to a highly disorganized form ofenergy, which cannot be converted back to the paddle wheel as the rotationalkinetic energy. Only a portion of this energy can be converted to workby partially reorganizing it through the use of a heat engine. Therefore,energy is degraded during this process, the ability to do work is reduced,molecular disorder is produced, and associated with all this is an increase inentropy.The quantity of energy is always preserved during an actual process (thefirst law), but the quality is bound to decrease (the second law). Thisdecrease in quality is always accompanied by an increase in entropy. As anexample, consider the transfer of 10 kJ of energy as heat from a hot mediumto a cold one. At the end of the process, we still have the 10 kJ of energy,but at a lower temperature and thus at a lower quality.Heat is, in essence, a form of disorganized energy, and some disorganization(entropy) flows with heat (Fig. 7–25). As a result, the entropy and thelevel of molecular disorder or randomness of the hot body decreases withthe entropy and the level of molecular disorder of the cold body increases.The second law requires that the increase in entropy of the cold body begreater than the decrease in entropy of the hot body, and thus the netentropy of the combined system (the cold body and the hot body) increases.That is, the combined system is at a state of greater disorder at the finalstate. Thus we can conclude that processes can occur only in the directionof increased overall entropy or molecular disorder. That is, the entire universeis getting more and more chaotic every day.Entropy and Entropy Generation in Daily LifeThe concept of entropy can also be applied to other areas. Entropy can beviewed as a measure of disorder or disorganization in a system. Likewise,entropy generation can be viewed as a measure of disorder or disorganizationgenerated during a process. The concept of entropy is not used in dailylife nearly as extensively as the concept of energy, even though entropy isreadily applicable to various aspects of daily life. The extension of theentropy concept to nontechnical fields is not a novel idea. It has been thetopic of several articles, and even some books. Next we present several ordinaryevents and show their relevance to the concept of entropy and entropygeneration.Efficient people lead low-entropy (highly organized) lives. They have aplace for everything (minimum uncertainty), and it takes minimum energyfor them to locate something. Inefficient people, on the other hand, are disorganizedand lead high-entropy lives. It takes them minutes (if not hours)to find something they need, and they are likely to create a bigger disorderas they are searching since they will probably conduct the search in a disorganizedmanner (Fig. 7–26). People leading high-entropy lifestyles arealways on the run, and never seem to catch up.You probably noticed (with frustration) that some people seem to learnfast and remember well what they learn. We can call this type of learning