Thermodynamics_2

Thermodynamics_2 - CRITERIA CRITERIA FOR SPONTANEITY H S...

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CRITERIA FOR SPONTANEITY H Exothermic reactions ( H <0) are usually spontaneous. S t i f Spontaneous if S system + S surroundings > 0 We need a new state function that can predict spontaneity. This is called the Free Energy : G = H T S T is absolute temperature (in K). G refers to a reaction at constant T and P. Criteria for spontaneity G < 0 Spontaneous G > 0 Not spontaneous G = 0 System at equilibrium.
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Potential Energy and Free Energy
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STANDARD FREE ENERGY OF FORMATION G f ° Free energy change in forming one mole of a compound from its elements each in their standard states. Standard States: Units: Solid Pure solid Liquid Pure liquid G f ° : kJ/mole kJ/mole Gas 1 atm pressure Solution 1M solution Elements G ° = 0 H f ° : S ° : J/mole-K f Temperature Usually 25 ° C STANDARD FREE ENERGY OF REACTION: G ° rxn =  G f ° (products)  G f ° (reactants)
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STANDARD FREE ENERGY For other temperatures: rxn rxn T rxn H° and S° do not vary much with T, BUT G° does!!!
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Thermodynamics_2 - CRITERIA CRITERIA FOR SPONTANEITY H S...

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