l06 - 20.110J 2.772J 5.601J Thermodynamics of Biomolecular...

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20 .110/5.60 Fall 2005 Lecture #6 page 1 The Second Law First Law showed the equivalence of work and heat for cyclic process ⇒= q w = + = 0 , dU U Suggests engine can run in a cycle and convert heat into useful work. Second Law Puts restrictions on useful conversion of to Follows from observation of a directionality to natural or spontaneous processes Provides a set of principles for - determining the direction of spontaneous change - determining equilibrium state of system Need a definition: Heat reservoir Definition : A very large system of uniform T , which does not change regardless of the amount of heat added or withdrawn. Also called a heat bath . Real systems can come close to this idealization. Two classical statements of the Second Law: Kelvin Clausius and a Mathematical statement 20.110J / 2.772J / 5.601J Thermodynamics of Biomolecular Systems Instructors: Linda G. Griffith, Kimberly Hamad-Schifferli, Moungi G. Bawendi, Robert W. Field
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20 .110/5.60 Fall 2005 Lecture #6 page 2 I. Kelvin : It is impossible for any system to operate in a cycle that takes heat from a hot reservoir and converts it to work in the surroundings without at the same time transferring some heat to a colder reservoir. T 1 (hot) q q w >0 <0 -w= q -w IMPOSSIBLE!! T 1 T 2 (c old) q 1 q q 1 2 w qw q 1 2 =- - -w -q 2 OK!! II. Clausius : It is impossible for any system to operate in a cycle that takes heat from a cold reservoir and transfers it to a hot reservoir without at the same time converting some work into heat. q q 2 1 -= qq 12 T 1 T 2 1 q 2 q w> q 2 1 0 -=+ qwq 1 2 T 1 T 2 1 w q 2 Alternative Clausius statement : All spontaneous processes are irreversible. (e.g. heat flows from hot to cold spontaneously and irreversibly) 20.110J / 2.772J / 5.601J Thermodynamics of Biomolecular Systems Instructors: Linda G. Griffith, Kimberly Hamad-Schifferli, Moungi G. Bawendi, Robert W. Field
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20 .110/5.60 Fall 2005 Lecture #6 page 3 Mathematical statement : 0 0 < = T q and irrev rev đ đ đ rev is a state function đ =→ = rev dS S ENTROPY ∫∫ > = = = 2 1 2 1 1 2 0 for cycle ⎯⎯⎯
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This note was uploaded on 11/11/2011 for the course BIO 20.010j taught by Professor Lindagriffith during the Spring '06 term at MIT.

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l06 - 20.110J 2.772J 5.601J Thermodynamics of Biomolecular...

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