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Chap_20 - Chapter 20 Thermodynamics In this chapter we turn...

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350 Chapter 20 Thermodynamics In this chapter we turn our attention to what it is that causes events of any kind, whether they be physical or chemical, to occur spontaneously—that is, by themselves without outside assistance. Spontaneous events are crucial for our existence, because without them nothing would ever happen and we wouldn’t exist. Understanding the factors that contribute to spontaneity is important because such events provide the driving force for all natural changes. You will also learn that there is a close connection between thermodynamics and chemical equilibrium. Learning Objectives As you study this chapter, keep in mind the following objectives: 1 To learn what thermodynamics means and to discover the kinds of questions it seeks to answer. 2 To learn how thermodynamics deals with the exchange of energy between a system and its surroundings. 3 To review the concepts of internal energy and enthalpy and the heats of reaction at con- stant volume and at constant pressure. 4 To learn how to convert between E and H for a chemical system. 5 To learn what a spontaneous change is and how everything that happens can be traced to some spontaneous change somewhere. 6 To learn what influence energy changes have on the tendency for an event to occur spon- taneously. 7 To learn the meaning of the term entropy, S , and to see how an entropy increase favors a spontaneous change. 8 To learn how entropy changes can be calculated from absolute entropies. 9 To learn how the Gibbs free energy, G , interrelates the energy and entropy factors in de- termining the spontaneity of a chemical or physical change. 10 To learn how to calculate standard free energy changes from H ° and S ° and from stan- dard free energies of formation. 11 To learn what relationship exists between the free energy change and the work that is available from a chemical reaction. 12 To see how free energy is related to equilibrium. 13 To learn how G ° can be used to predict the outcome of a chemical reaction. 14 To learn to compute equilibrium constants from thermodynamic data, and vice versa.
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Chapter 20 351 20.1 Internal energy can be transferred as heat or work, but it cannot be created or destroyed Review Thermodynamics is the study of energy changes, with a focus on the way energy flows between system and surroundings. Studying thermodynamics allows us to understand why spontaneous events occur and gives us insight into answers to many questions that plague modern society. In this section, we review some topics introduced in Chapter 7. The first law of thermodynamics is given by the equation E = q + w where q is the heat absorbed by the system and w is the work done on the system . Study the signs of q and w in relation to the direction of energy flow.
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