Question

MCAT Tutorial: Introduction to Electrochemistry

Answer 1

\({\bf{Basic~Terminology:}}\)
- electrochemical cell: chemical reaction in solution(s) that are linked with electrodes in electrolytes
- galvanic cell: generates current
- electrolytic cell: uses current
- anode: the positive electrode, where oxidation takes place
- cathode: the negative electrode, where reduction takes place
- oxidation: chemical loses electrons [the charge goes up]
- reduction: chemical gains electrons [the charge is reduced]

Cell Notation:

oxidation on the left, reduction on the right

so for the rxns

Zn(s) --> Zn(2+) + 2e- (losing electrons, thus oxidation)
Cu(2+) + 2e- --> Cu(s) (gaining electrons, thus reduction)

we can re-write this as

Zn(s) | Zn^(2+) || Cu^(2+) | Cu(s)

ions go in the middle, separated by the double bar to represent the salt bridge

Answer 2

\({\bf{Formulas~to~Know:}}\)

W= -nFE

F = faraday's constant
E = cell potential/voltage
n = # of moles electrons

applying this to Gibb's free energy we get

ΔG = -nFE
where ΔG > 0 indicates nonspontaneity and negative electric potential
ΔG < 0 indicates spontenaity and positive electric potential

Ecell = Ecathode - Eanode
cell potential/voltage
typically you will be given the reduction potentials, to obtain the oxidation potential simply multiply by (-1)

**** important note: when adding reactions it is important to balance the # of electrons by multiplying the equations by an integer value BUT you do NOT multiply the electric potentials by that value

Nernst Equation: Ecell = E° - RT/nF * [lnQ]
E° is the standard potential, Ecell is the potential at the conditions being studied, R is the ideal gas constant (usu. 8.314 J/molK) if we are working with joules, T is temp. in Kelvin, n is # of moles, F is faraday's as usual, Q is the reaction quotient

Answer 3

basic structure of an electrochemical cell, notice the salt bridge to allow ions to flow, preventing charge from accumulating on one cell and stopping the flow of electrons

Answer 4

Anyway, that's the end of my tutorial, I hope it was a helpful resource. Source material is the 2nd Edition Barron's Prep book for the new MCAT