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Chapt18

Accounting

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Back Forward Main Menu TOC Study Guide TOC Textbook Website MHHE Website
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C H A P T E R 18 Entropy, Free Energy, and Equilibrium T HERMODYNAMICS IS AN EXTENSIVE AND FAR - REACHING SCIENTIFIC DIS - CIPLINE THAT DEALS WITH THE INTERCONVERSION OF HEAT AND OTHER FORMS OF ENERGY . T HERMODYNAMICS ENABLES US TO USE INFORMA - TION GAINED FROM EXPERIMENTS ON A SYSTEM TO DRAW CONCLUSIONS ABOUT OTHER ASPECTS OF THE SAME SYSTEM WITHOUT FURTHER EX - PERIMENTATION . F OR EXAMPLE , WE SAW IN C HAPTER 6 THAT IT IS POS - SIBLE TO CALCULATE THE HEAT OF REACTION FROM THE STANDARD EN - THALPIES OF FORMATION OF THE REACTANT AND PRODUCT MOLECULES . T HIS CHAPTER INTRODUCES THE SECOND LAW OF THERMODYNAMICS AND THE G IBBS FREE - ENERGY FUNCTION . I T ALSO DISCUSSES THE RELATION - SHIP BETWEEN G IBBS FREE ENERGY AND CHEMICAL EQUILIBRIUM . 18.1 THE THREE LAWS OF THERMODYNAMICS 18.2 SPONTANEOUS PROCESSES AND ENTROPY 18.3 THE SECOND LAW OF THERMODYNAMICS 18.4 GIBBS FREE ENERGY 18.5 FREE ENERGY AND CHEMICAL EQUILIBRIUM 18.6 THERMODYNAMICS IN LIVING SYSTEMS 725 Back Forward Main Menu TOC Study Guide TOC Textbook Website MHHE Website
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A spontaneous reaction does not necessarily mean an instantaneous reaction. In Chapter 6 we encountered the first of three laws of thermodynamics, which says that energy can be converted from one form to another, but it cannot be created or de- stroyed. One measure of these changes is the amount of heat given off or absorbed by a system during a constant-pressure process, which chemists define as a change in en- thalpy ( H ). The second law of thermodynamics explains why chemical processes tend to fa- vor one direction. The third law is an extension of the second law and will be exam- ined briefly in Section 18.3. One of the main objectives in studying thermodynamics, as far as chemists are con- cerned, is to be able to predict whether or not a reaction will occur when reactants are brought together under a special set of conditions (for example, at a certain tempera- ture, pressure, and concentration). This knowledge is important whether one is syn- thesizing compounds in a research laboratory, manufacturing chemicals on an indus- trial scale, or trying to understand the intricate biological processes in a cell. A reaction that does occur under the given set of conditions is called a spontaneous reaction. If a reaction does not occur under specified conditions, it is said to be nonspontaneous. We observe spontaneous physical and chemical processes every day, including many of the following examples: A waterfall runs downhill, but never up, spontaneously. A lump of sugar spontaneously dissolves in a cup of coffee, but dissolved sugar does not spontaneously reappear in its original form. Water freezes spontaneously below 0°C, and ice melts spontaneously above 0°C (at 1 atm).
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