武汉大学：《物理化学 Physical Chemistry》课程教学资源（PPT课件讲稿）09 chemical potential

溶宝置 Idea Develops the concept of chemical potential and shows how it can be used to account for the equilibrium composition of chemical reaction Equilibrium composition Th hemodynamic under any reaction formulations conditions

Idea: Develops the concept of chemical potential and shows how it can be used to account for the equilibrium composition of chemical reaction. Thermodynamic formulations Equilibrium composition under any reaction conditions

dynamic equilibrium"--a chemical reaction moves toward a dynamic equilibrium in which both reactants and products are present but have no further tendency to undergo net change spontaneous chemical reaction''--the direction of spontaneous change at constant temperature and pressure is towards lower values of the gibbs energy g

“dynamic equilibrium” -- a chemical reaction moves toward a dynamic equilibrium in which both reactants and products are present but have no further tendency to undergo net change. “spontaneous chemical reaction” -- the direction of spontaneous change at constant temperature and pressure is towards lower values of the Gibbs energy G

equilibrium"=The Gibbs energy minimum a bB isomerization: pentane to 2-methylbutane e. g conversion: L-alanine to d-alanine +d5 A lB=+5 the extent of reaction

“equilibrium” = “The Gibbs energy minimum” A  B isomerization: pentane to 2-methylbutane conversion: L-alanine to D-alanine e.g., –d +d dnA = –d dnB = +d “the extent of reaction

the reaction Gibbs energy'--is defined as the slope of the graph of the gibbs energy plotted against the extent of reaction △G=/G aE P T difference vs. derivative?

“the reaction Gibbs energy” -- is defined as the slope of the graph of the Gibbs energy plotted against the extent of reaction , r P T G G      =      difference vs. derivative?

A proof: A reaction advances by ds, the change in G is dG=uAna ubdnB OG B A -HAdE uBdE 5 PT (μB-A 1B=1 1 Chemical potentials vary with composition, A G changes as the reaction proceeds d The reaction runs in the direction of decreasing G

A proof: A reaction advances by d, the change in G is: dG = AdnA + BdnB = –Ad + Bd = (B – A)d , B A P T r B A G G           = −     = − ¶Chemical potentials vary with composition, rG changes as the reaction proceeds; ¶ The reaction runs in the direction of decreasing G

Ha> HB: the reaction a-B is spontaneous uB>HA: the reaction B>A is spontaneous ua- uB: neither direction, A,G=0 65 △G0 △G=0 Extent of reaction, 5

A > B : the reaction A→B is spontaneous B > A : the reaction B → A is spontaneous A = B : neither direction, rG = 0 Extent of reaction,  Gibbs energy, G rG 0 rG = 0

AG0, the reverse reaction is spontaneous, called endergonic"(work consuming, e.g., eletrolysing water to H, and O2) G=0, reaction at equilibrium, neither exergonic nor endergonic

rG 0, the reverse reaction is spontaneous, called “endergonic” (work consuming, e.g., eletrolysing water to H2 and O2 ) rG = 0, reaction at equilibrium, neither exergonic nor endergonic

Perfect Gas Equilibria △G=pB-FA (uB+RTin PB)-(A+RTIn pa =△G+RTln2B PA =△G°+ RTIn Q 0, pure A reaction guotient oo, pure B

Perfect Gas Equilibria ( ln ln ) ( ) ln ln r B A B B A A B r A r G RT P RT P P G RT P G RT Q          = − = + − +   =  +     =  + “reaction quotient” 0, pure A , pure B

The Standard Reaction Gibbs Energy, AGo Like the standard reaction enthalpy, defined as the difference in the standard molar gibbs energies of the reactants and products B =△G-△G0

The Standard Reaction Gibbs Energy, rG Like the standard reaction enthalpy, defined as the difference in the standard molar Gibbs energies of the reactants and products. r B m A m , , f B f A G G G G G       = − =  − 

At equilibrium,△G=0, 0=△G6+ rTIn k RT In K=-△G K=(PR/PA B Equilibrium equilibrium tables of constant thermodynamic data

At equilibrium, rG = 0, 0 = rG + RT ln K RT ln K = – rG K = (PB /PA)equilibrium tables of thermodynamic data equilibrium constant