[briteyellowness]

if i have a galvanic cell connected to a lightbulb, (say that gold is being reduced at the cathode and chloride is being oxidized at the anode), when will the lightbulb burn out?

i thought one reason could be that the gold ions would be used up and if there was nothing let to reduce, the flow of electrons would stop, but the answer was when the reaction reaches equilibrium.  when does this reaction ever reach equilibrium?  i thought that the standard reduction potential is intrinsic regardless of the concentration so that there will always be an electromotive force Unless either the anode runs out, the cathode runs out, or the salt bridge runs out.  thanks for your help.

[sdekivit]

when equilibrium is reached E = 0 V. Nett nothing happens so there's no voltage of the cell. This is expressed in the law of Nernst:

E = E(0) - (RT/nF)ln K*


Your answr is correct too. When one of the reactants is used, no reaction occurs and thus E=0 too. Also the electrodes can be affected by the solid gold on it.

[briteyellowness]

so concentration does count when i'm trying to find the E in a galvanic cell?  i was always taught just to add/subtract the standard reduction potential.  when do i know i'm supposed to factor in concentration?  and does that mean if i start from standard conditions, since my concentrations will start changing, it means i will start shifting closer and closer to equilibrium and to E = 0 if none of my anodes or electrodes ran out before then?

[Donaldson Tan]

always taught just to add/subtract the standard reduction potential.

you only add/substract the standard reduction potential if and only if you are working with at standard condition, ie. STP and all aq species 1.0M