Equilibrium(cont'd At equilibrium no net current flows i e △E=0→i=0 However, there will be a dynamic equilibrium at electrode surface 0+e=R R-ne=o both processes will occur at equal rates so no net change in solution composition
Equilibrium (cont’d) At equilibrium, no net current flows, i.e., E = 0 i = 0 However, there will be a dynamic equilibrium at electrode surface: O + ne- = R R - ne- = O both processes will occur at equal rates so no net change in solution composition
Current Density Since i is dependent on area of electrode We normalize currents and examine I=j/A we call this current density So at equilibrium i=0=in H/A=-ICA= IA Which we call the exchange current density Note: by convention ia produces positive current
Current Density, I Since i is dependent on area of electrode, we “normalize currents and examine I = i/A we call this current density So at equilibrium, I = 0 = iA + iC ia /A = -i c /A = IA = -Ic = Io which we call the exchange current density Note: by convention iA produces positive current
Exchange Current Density Significance? Quantitative measure of amount of electron transfer activity at equilibrium ho large much simultaneous ox/red electron transfer(ET → inherently fast E「( kinetics) Io small little simultaneous ox/red electron transfer(E o sluggish ET reaction( kinetics)
Exchange Current Density Significance? Quantitative measure of amount of electron transfer activity at equilibrium Io large much simultaneous ox/red electron transfer (ET) inherently fast ET (kinetics) Io small little simultaneous ox/red electron transfer (ET) sluggish ET reaction (kinetics)
Summary: Equilibrium Position of equilibrium characterized electrochemically by 2 parameters egbm-equilibrium potential, Eo o exchange current density
Summary: Equilibrium Position of equilibrium characterized electrochemically by 2 parameters: Eeqbm - equilibrium potential, Eo Io - exchange current density
How Does I vary with E? Lets consider case 1: at equilibrium case 2: at E more negative than Eeabm case 3: at E more positive than Eeabm
How Does I vary with E? Let’s consider: case 1: at equilibrium case 2: at E more negative than Eeqbm case 3: at E more positive than Eeqbm