The Second and Third Laws of Thermodynamics Entropy

There are two principal physical statements of the second law of thermodynamics (1) If a system undergoes a cyclic process it cannot turn heat put into the system completely into work done on the surroundings. (2) Heat cannot flow spontaneously from a cooler to a hotter object if nothing else happens. 

The second law implies that no heat engine can have an efficiency as great as unity. 

The mathematical statement of the second law estahlishes a new state function, the entropy, denoted hy S and defined through its differential hy 

The mathematical statement of the second law provides a means of calculating the entropy change of any process that begins and ends at equilibrium states. 

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The second and third laws of thermodynamics The second law and the definition of entropy... 

In this chapter, we show that spontaneous processes are ones in which the entropy of the universe (system and surroundings) increases, and that for reversible processes, the total entropy change of the universe is zero. These conclusions lead us to the second and third laws of thermodynamics. 

The second and third law of thermodynamics can be understood in terms of the disorder concept of entropy. For an isolated system in which there is no transfer of mass or energy, a spontaneous change can be thought of as a change in which the particles of the system access more possible arrangements. That is, for a spontaneous process from state 1 to state 2,... 

This chapter has been a survey of the second and third laws of thermodynamics. We have used the Carnot cycle to introduce the concepts of entropy and efficiency, but the most important relationship we found was that = T dS. Together with the first law that led to eight very important... 

Why Do We Need to Know This Material The second law of thermodynamics is the key to understanding why one chemical reaction has a natural tendency to occur bur another one does not. We apply the second law by using the very important concepts of entropy and Gibbs free energy. The third law of thermodynamics is the basis of the numerical values of these two quantities. The second and third laws jointly provide a way to predict the effects of changes in temperature and pressure on physical and chemical processes. They also lay the thermodynamic foundations for discussing chemical equilibrium, which the following chapters explore in detail. 

In the previous chapter, we saw that entropy is the subject of the Second Law of Thermodynamics, and that the Second Law enabled us to calculate changes in entropy AS. Another important generalization concerning entropy is known as the Third Law of Thermodynamics. It states that ... 

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