Chem1202PReviewCh19 - Chemistry 1202 Review/Preview Chapter...

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Chemistry 1202 Review/Preview Chapter Nineteen Review Guide Dr. Saundra McGuire Spring 2007 Director, Center for Academic Success Adj. Prof., Dept. of Chemistry Thermodynamics IMPORTANT NOTE: Chapter 19 assumes mastery of the material in Chapter 5. The Chapter 19 problems require the application of the principles learned in Chapter 5. The Chapter 5 review guide provided in the Chem 1202 Review/Preview session should be thoroughly reviewed before the study of Chapter 19. I. Spontaneous Processes Spontaneous processes proceed on their own without any external assistance. The process that is the reverse of a spontaneous process is always non- spontaneous. The spontaneity of a chemical reaction generally depends on the temperature, pressure, and composition of the reaction mixture. A spontaneous process can occur at a rapid rate or at a rate that is so slow it is impossible to tell that a change is occurring. A process is at equilibrium if the forward and reverse processes are occurring at the same rate and there is not preference for either the forward or the reverse process. Thermodynamics tells us the direction and extent of a chemical process, but does not indicate how fast the reaction will occur. (See pages 803-808 of the text for an in depth discussion of this concept.) II. Entropy and the Second Law of Thermodynamics A. Entropy change The entropy is the amount of randomness or disorder in a system, and is a characteristic of the state of the system. The entropy of a gas is greater than that of a liquid, which is greater than that of a solid. The entropy change of a process, S can be determined from the initial and final entropy values as follows: S = S final – S initial When a process occurs at constant temperature (an isothermal process), S is related to the heat that would be transferred in the reversible process divided by the temperature (in kelvins), as follows: S = q rev /T Spontaneous reactions are often ones in which there is an increase in the entropy of the system (e.g. ice melting at 273 K), but not always. Systems tend to move toward an increase in disorder because a random state is more probable than an ordered one. B.
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Chem1202PReviewCh19 - Chemistry 1202 Review/Preview Chapter...

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