electrode potential

half cells = ?

half equation which contains non metals

what is the most common half cells

Hydrogen gas with H+ or uses platinum

what are the standard conditions ?

100 KPa , 298 K and 1.00 mol dm-3 soulatioms

some solutions will have variable oxidation states

Fe 2+ or Fe3+

direction of the electrons will depend on ?

on other half cells in the circuit.

before the potential of any half cell could be measured, a potential assigned to one particular half cell

electrode chosen was standard hydrogen electrode ( SHE ) and this electrode is assigned the potential of 0 volts

SHE

is a primary standard as it’s the potential to which all others are compared.

standard hydrogen electrode

H2(g) 298K / 100 kPa / 1.00 mole dm-3 → Pt electrode allow equilibrium between H2 and H+

assigned an electrode potential E0 of 0.00 V

2H+ (aq) + e- ↔ H2(g) reduction

Pt electrode provide a sink / source of electrons , which go through a conductor “ metal”

connect SHE to another electrode to records the potential difference ( voltage )

standard electrode potential def

The SEP or E° of a system is defined as the measured potential difference between the two electrodes of a cell in which the potential of the electrode of interest is measured relative to the standard hydrogen electrode and in which all the chemical species have a concentration of 1M.

representing cells

most positive on right

Reduced | oxidised || oxidised | reduced

ROOR

vertical line separate phases double line for salt bridge insert metals on the outside.

calculating electrode potential

E0 cell = E0 RHS - E0 LHS

results should be positive for the reaction to be feasible or spontaneous.

Combining half cells together

• Before the potential of any half-cells could be measured, a potential had to be assigned to one particular half-cell (then the potential of all the other electrodes could be measured against it).

When two half cells are combined together the resulting electrochemical cell has:

• a positive terminal;

• a negative terminal.

• The half cell with the more positive electrode potential becomes the positive terminal and electrons flow towards it.

factors that affect the electrode potential

temp, con.c and pressure

standard electrode potential

more negative = stronger reducing agent, easier to lose electrons

go most easily from right to left

Most negative electrode in a cell will always produced the electrons.

add pic

add exam QUESTIONS