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Lecture 13

CHEM 205 Lecture 13

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CHEM 205
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CHEM 205 -lecture 12” PS2 #9, See notes in notebook Lecture 13: Explanation of what Gibbs Free Energy really is • For equation ΔG®=-RTlnK, units end up as J/mol o Can modify this to just J by using ΔG®=-RTlnK *1mol • Things to remember: o Cv=3/2RT=dU/dT • Definition of Gibbs Free Energy: max amount of energy that can be used to do useful work that is NOT Expansion work. o Achieved only when all 3 conditions are met: Constant T, P of system, and REVERSIBILITY  (max W, q always achieved from reversible conditions) o Thus, when ΔG=0, the ability for useful work is 0, example would be a dead battery • Gibbs equation can be used to find the temperature at which a reaction changes from spontaneous to nonspontaneous and vice versa: o ΔG= ΔH-T ΔS…Thus, T= ΔH/ ΔS at which equilibrium temperature is achieved  This makes sense since at this temperature, ΔG=0, rearranging the initial equation gives that. • Derivation of Free Energy and Work: (aka, how did we get that definition of Gibbs free energy from above?) o dG=dH-TdS-SdT  to make it easier for us, let us define T=constant, this simplifies equation to: o dG=dH-TdS  we know U=q+w and thus H=U-w=U+PVwork, so we can write equation as: o dG=dU+PdV + VdP – TdS  to simplify, let us define P=constant for the system (which must also equal outside P. This sim
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