Electrochemistry3+4 Flashcards
How (when) is Ecell measured?
Ecell = max voltage, measured with no current flowing (no energy loss to heat)
Voltaic cells and work on the surroundings
Voltaic cells release energy or “do work on the surroundings”
Formula for charge
charge = zF
where:
z is the number of mol e-
F is the “Faraday Constant”, charge of 1 mol e-, 96 485 Coulombs
Nernst Equation for Ecell
Ecell = E°cell – (RT/zF) lnQ
Nernst Equation, Effect of Q
Q < 1
Ecell > E°cel
Nernst Equation, Effect of Q
Q = 1
Ecell = E°cel
Nernst Equation, Effect of Q
Q > 1
Ecell < E°cel
What is ELECTROLYSIS?
ELECTROLYSIS: breaking of bonds (lysis) by input of electrical energy
Commonly used to decompose compounds into constituent elements
Anode, cathode and electrolyte for MOLTEN SALTS
Anode = anion (oxidized) Cathode = cation (reduced) Electrolyte = molten salt
anode, cathode and electrolyte for “PURE” WATER
why “PURE”? -> because some salt has been sparingly added to the pure water
Anode = formation of O2 (oxidation of oxygen in water)
Cathode = formation of H2 (reduction of hydrogen in water)
Electrolyte = dilute aqueous salt solution (inert salts added to increase conductivity)
anode, cathode and electrolyte for AQUEOUS SALT SOLUTIONS
Anode = most easily oxidized species, anion/H2O (most negative Ehalfcell) Cathode = most easily reduced species, cation/H2O (most positive Ehalfcell) Electrolyte = aqueous salt solution
Faraday’s Law of Electrolysis
The amount of substance produced at each electrode is directly proportional
to the quantity of charge flowing through the cell
E°cell>0
E°cell>0: the reaction is spontaneous and it is a voltaic cell.
E°cell<0
E°cell<0: the reaction is non-spontaneous and it is referred to as an electrolytic cell.
E° for SHE (Standard Hydrogen Electrode)
(eqn is:) 2H+ + 2e- —> H2
E°=0 V (no electrical potential at SHE)
