Chapter_19-Thermodynamics

Chapter_19-Thermodynamics - Ch.19 Thermodynamics Chemical...

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Chemical thermodynamics Ch.19. Thermodynamics Heat Force
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First law of thermodynamics Ch.19. Thermodynamics E = q + w Change of the internal energy of the system Heat transferred to the system from the environment The work the system has done on the environment (The first law of thermodynamics is the one of the forms of the law of energy conservation). In other words: all energy lost by the system is gained by the surrounding and vice versa.
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Spontaneous and nonspontaneous processes Ch.19. Thermodynamics Expansion of a gas is a spontaneous process A spontaneous process is the one that proceeds on its own without any outside assistance. Processes that are spontaneous in one direction are nonspontaneous in the opposite direction. Accumulation of a gas in one of the vessels is a nonspontaneous process Exothermal processes are often (but not always) spontaneous.
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Spontaneity and conditions Ch.19. Thermodynamics The process that is spontaneous at some temperature can be nonspontaneous at different temperature. Freezing Melting (at T=0 : equilibrium)
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Spontaneity and the system definition Ch.19. Thermodynamics To answer the question if a process is spontaneous we have to consider what is included into the system Spontaneous Nonspontaneous Spontaneous First law of the thermodynamics cannot predict the direction of a process.
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Reversible and irreversible processes Ch.19. Thermodynamics In a reversible process a system and surroundings can be restored to their original state by exactly reversing the change. Reversible processes are those that reverse direction whenever an infinitesimal change is made in some property of the system. Reversible process is a model.
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Reversible and irreversible processes Ch.19. Thermodynamics All real processes are irreversible. Real processes cannot happen infinitely long a) b) c) Expansion of a gas – is a spontaneous process
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Entropy and entropy change Ch.19. Thermodynamics Entropy S is one of the state functions of a system – it does not depend upon the path. Entropy change: S = S final S initial Entropy from one side is a measure of randomness of a system. Entropy change from the other side can be defined as a heat transferred to the system at constant temperature in a reversible process: T q S rev = (at T =constant) Unit of entropy is J/K
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S for phase changes Ch.19. Thermodynamics Phase change happens at constant temperature, thus it is an example of a process where calculation of S is the simplest. Example: melting of 1 mol of ice ( H fusion = 6.01 kJ/mol) K J K mol J mol T H T q S fusion rev / 0 . 22 273 ) / 10 01 . 6 )( 1 ( 3 = × = = =
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S for gas volume change Ch.19. Thermodynamics (For isothermal processes only ( T =const during the process)) ) ln( ) ln( 1 2 1 2 V V nR T V V nRT T q S rev = = = V 1 V 2 R= 8.314 J/(mol K) Initial Final Very slow, isothermal expansion
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Second law of thermodynamics Ch.19. Thermodynamics (Second law helps us to tell which direction the process will go, or in other
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This note was uploaded on 01/02/2012 for the course CHEM 114 taught by Professor Sergeiaksyonov during the Fall '11 term at ASU.

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Chapter_19-Thermodynamics - Ch.19 Thermodynamics Chemical...

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