Electrochemistry Notes

Electrochemistry

I. Voltaic (Galvanic) Cells:
a. spontaneous redox reactions generate electrical current
b. alf cells are a metal electrode immersed in a solution of one of its ions
c. oltaic cells have two half-cells (one for the reduction and one for the oxidation reaction)
1. “An Ox”   Anode oxidation
2. “Red Cat”   Reduction Cathode
d.   salt bridge is an inverted u-shaped tube which contains a non-reactive electrolyte and connects the two half-cells
1. allows the migration of ions to balance the charge
e. he difference in potential energy between the anode and the cathode of the cell is the Cell potential (Ecell)
II. Cell diagrams
a. 
b. electrodes can be inert: they just serve to give a surface to establish the electrical potential
III. Standard Cell Potential (E0cell)
a. E0(cell) = E0(cathode) + E0(anode)
b. positive E0cell means a spontaneous reactions, and negative is nonspontaneous
c. 0 E0cell means the reaction is at equilibrium
IV. Equilibrium and Spontaneity
a.  :   n=number of moles of electrons transferred
    f=faraday constant(96500 coulombs per mole of electrons)
b. Nernst Equation: use to find cell voltage for nonstandard conditions
1. 
V. Electrolytic Cells
a. an electrical current from an external source is passed through an electrochemical cell and causes a nonspontaneous reaction to occur : electrolysis
b. Due to the external source that is controlling the flow of electrons, the polarities of the electrodes are the opposite of those in voltaic cells
1. the anode of an electrolytic cell has a positive charge and the cathode has a negative charge
c. Overvoltage is the excess voltage above the calculated E values that must be applied in   order for the reactions to occur
VI. Quantitative Electrolysis
a.    :   I=current (amperes) q=charge (coulombs) t=time (seconds)