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Lecture 6 Free Energy, Equilibrium and Reaction Direction

Lecture 6 Free Energy, Equilibrium and Reaction Direction -...

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Review from last lecture: Free Energy Gibbs Free Energy Change ( G ): evaluates spontaneity as a function of enthalpy and entropy of the system . G sys = H sys T S sys G < 0 Process is spontaneous G = 0 Process is at equilibrium G > 0 Process is non spontaneous The sign of G reveals whether a reaction is spontaneous, but as we will discuss later today, the magnitude of G tells how spontaneous (how favorable) it is.
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Standard Free Energy ( G ˚ rxn ) is the free energy for a reaction occurring under standard state conditions. Reactants in their standard states are converted to products in their standard states. G ˚ ƒ is the standard free energy of formation of a compound from its elements in their standard states. As is the case for H and S, G is a state property and an extensive property, such that: G ˚ rxn = m G ˚ ƒ (products) n G ˚ ƒ (reactants) Gibbs Free Energy G ˚ ƒ have similar properties to H ˚ ƒ is the values: G ˚ ƒ of an element in its standard state is ZERO reversing a reaction changes the sign of G ˚ ƒ
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Gibbs Free Energy: Sample Calculation Calculate the standard free energy change for the following reaction. 4 NH 3 (g) + 5 O 2 (g) 4 NO(g) + 6 H 2 O(l) = -1010.8 kJ
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