Electrode Potentials

a device capable of generating a potential difference from redox reactions

in 1 half cell, the oxidation reaction occurs, and in the other half cell, the reduction reaction occurs

1.00 mol dm-3

• half cells always contain an element in 2 different oxidation states • here, copper is in the 0 and +2 oxidation states • in the cell, the ions from the solution are being reduced and the metal is being oxidised. This establishes an equilibrium between the 2 oxidation states • its convention to have the forward reaction as the the ions gaining electrons (reduction)

to ensure the reaction has a surface to occur on- it allows electrons to be transferred. -In this half-cell, the gas has a standard pressure of 100KPa

• its inert, so it doesn’t react with anything in the cell • it conducts electricity, allowing electrons to be lost or gained • its coasted in platinum black, which has a large surface area

a solid surface which allows the transfer of electrons to and from it

• the half- cell has an equimolar solution (equal concentrations) of Fe2+ and Fe3+ ions and a platinum electrode • the platinum electrode is necessary as it provides a surface on which electrons can be transferred between the 2 iron species an equilibrium is established between the different oxidation states Fe3+ (aq) + e- ⇌ Fe2+ (aq)

• further left = better at donating electrons (the species is itself oxidised • further right = is better at accepting electrons (he species is itself reduced -he position of equilibrium is measured by the standard electrode potential

the voltage measured under standard conditions when the half cell is connected to a standard hydrogen electrode

temp = 298K solution concentration = 10 moldm-3 pressure = 100kPa

• more positive = forward (reduction) and accepts electrons from the other half- cell. It becomes the positive terminal of the electrochemical cell • more negative = backwards (oxidation) and donates electrons to the other half- cell. It becomes the negative terminal of the electrochemical cell

to form a circuit

contains free ions to complete eh circuit so that charge can flow- its is made from filter paper soaked in KNO3 (aq)

gives the difference in standard electrode potentials of the half cells measured in volts -the voltmeter has an effectively infinite resistance, so when its connected to measure the voltage, the redox reaction will not actually occur as no current will flow - this means the maximum possible EMF can be recorded

0V its used as a reference

a list of standard electrode potentials of all the possible half- ells

E cell = E (positive terminal) - E (negative terminal) E cell = E (reduction) - E (oxidation)

• single line= phase boundary and if there’s no phase boundary, we use a comma. ionic cells always have a platinum electrode, which is represented by a phase boundary • a double line= salt bridge • the species with the high oxidation state= written next to salt bridge • the oxidation cell (-) goes on the left • the reduction (+) goes on the right

the greater the cell potential, the more feasible the reaction

• if the conditions are changed, this can change the position of equilibrium, and therefore can change the electrode potential • although it tells us about feasibility, it doesn’t tell us anything about kinetic factors such as activation energy and rate of reaction

• this reaction generates electrical energy until the chemicals within the battery have fully reacted • the battery is then disposed of -in a rechargeable battery, when the chemicals have reacted fully, a potential difference can be applied to the cell in the opposite direction, which will regenerate the original chemicals. This allows us to re- use the battery

• used in laptops and mobile phones • one of the electrodes in a lithium- ion battery is made of graphite, and the other is made of lithium cobalt oxide, LiCoO2 • the electrolyte for a lithium-ion battery is an organic solvent

• because fuel cells do not have a stock of chemical held in the electrodes or electrolyte • instead, the chemicals are stored externally and are fed into the cell when electricity is required