Chapter%2010-s - Thermodynamics is the only science about...

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OFP Chapter 11 1 11/12/2008 Thermodynamics is the only science about which I am firmly convinced that, within the framework of the applicability of its basic principles, it will never be overthrown - Albert Einstein
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OFP Chapter 11 2 11/12/2008 Chapter 11 Spontaneous Change and Equilibrium • 11-1 Enthalpy and Spontaneous Change • 11-2 Entropy • 11-3 Absolute Entropies and Chemical Reactions • 11-4 The Second Law of Thermodynamics • 11-5 The Gibbs Function • 11-6 The Gibbs Function and Chemical Reactions • 11-7 The Gibbs Function and the Equilibrium Constant • 11-8 The Temperature Dependence of Equilibrium Constants
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OFP Chapter 11 3 11/12/2008 WHAT DETERMINES THE DRIVING FORCE OF A REACTION? • WHY DO SOME REACTIONS HAVE LARGE K VALUES WHILE OTHERS HAVE VERY SMALL K VALUES ? • MANY REACTIONS THAT HAVE LARGE K VALUES(i.e. HAVE LARGE DRIVING FORCE) ARE ALSO EXOTHERMIC ( i.e. have large negative H r o values BUT NOT ALL. THERE MUST BE SOME OTHER STATE FUNCTION, what is it???
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OFP Chapter 11 4 11/12/2008 • Consider Energy, it is perhaps obvious that processes occur spontaneously to produce a state of lower energy and gives off energy (exothermic ) (Falling rock from the top of the hill to its bottom). • But, a chunk of ice at Room Temperature, spontaneously melts by absorbing heat (endothermic), forming a state of higher Energy(the liquid). Most of salts absorb heat when they spontaneously dissolve in water • Volatile solvents evaporate spontaneously and they do that by absorbing heat . • Apparently Some OTHER State Function is involved in determining the direction of spontaneous change in molecular systems besides internal energy or the enthalpy.
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OFP Chapter 11 5 11/12/2008 • This additional factor is the tendency of a system to assume the most random molecular arrangement possible. • Molecular Systems Like to become disordered and more random. • Natural processes occur spontaneously in the direction of Decreased Energy and Increased Entropy. ) ( 2 ) ( 2 s l State Ordered State Disordered O H S O H S S S Entropy > > =
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OFP Chapter 11 6 11/12/2008 Entropy is a quantitative measure of the number of microstates(W) available to the molecules in a system : S= k ln W (BOLTZMANN) Entropy measures the degree of randomness or disorder in a system • The Entropy of all substances is positive S solid < S liquid < S gas Δ S is the Entropy Change in a system • Entropy = S which has the units JK - 1 mol -1. FOR A CRYSTALLINE SOLID AT ZERO DEGREE, W=1, THEN S=0 Disorder and Entropy
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OFP Chapter 11 7 11/12/2008 Third Law of Thermodynamics THE ENTROPY OF ANY SINGLE CRYSTAL OF ANY SUBSTANCE(element or a compound) IS ZERO AT ABSOLUTE ZERO S = 0 at 0 ° K • This Enable us to determine the absolute Entropy of every Substance as follows: • As temperature increases above 0 K, molecular motion increases ,the Entropy increases and can be calculated as follows : • For a change in temperature between 0 and
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This note was uploaded on 09/04/2009 for the course CHEM 1310 taught by Professor Cox during the Spring '08 term at Georgia Institute of Technology.

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Chapter%2010-s - Thermodynamics is the only science about...

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