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Chapter 19 - chemical thermodynamics - outline 5-7-00

G represents the part of that total energy which can

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G represents the part of that total energy which can be harnessed to do useful work during the transfer, i.e., the energy "free" to do work From this we might say:  H =  G + "unfree" energy By now you might suspect--and correctly--that the "unfree" energy term involves what we have called the entropy  change,  S . We know that the entropy change of the system is connected to the entropy change of the surroundings  which is highly temperature dependent. Thus the relationship above is generally written as:  G o  =  H o  - T S o This is known as the  Gibbs-Helmholtz equation  and is the absolute bottom line in chemical thermodynamics. Sort  of.  Remember in our definition of  enthalpy (H)  we said it was a "state function". The net enthalpy change  ( H --which  is the only kind of enthalpy quantity we can measure) is  independent of path Effect of Temperature on Reaction Spontaneity G o                                         H o      S o          Reaction Characteristics example    (opposite is true for reverse reaction) always  negative          -        +        spontaneous at all temp       2O 3(g)    3O 2(g)
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