Electrode Potential
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define ‘standard electrode potential’
the potential difference between a half cell and the standard hydrogen electrode under standard conditions
standard electrode potential measurement conditions
298k 100kPa (gasses) 1 mol/dm^3 (solutions) 0A current (high resistance voltmeter used)
how is a standard electrochemical cell set up
the half cell with the most positive standard electrode potential on the right.
standard cell notation rules
most oxidised species near the centre most positive standard potential on the right platinum electrode if there’s no solid metal commas separate species if they have the same state (example:) Pt | H2 | H^+ || Fe^3+ , Fe^2+ | Pt
in an electrochemical cell, which species is oxidised and which is reduced
the species with the most positive standard electrode potential is reduced
components of an electrochemical cell (experiment to measure electrode potential)
High resistance voltmeter 2 half cells salt bridge
which electrode do the ions from a salt bridge move to
the positive ions move to the cathode. the negative ions move to the anode
in an electrochemical cell what determines which is the cathode and anode and which direction do electrons flow
the cathode is in the half cell with the most positive standard electrode potential. electrons flow from the anode to the cathode
how do you calculate the electrode potential of a cell
E(cell) = E(right) - E(left) (right and left refer to the position in the cell notation E is the standard electrode potential)
how does the standard electrode potential change with concentration (use a copper electrode as an example)
Cu^2+ + 2e^- Cu if Cu^2+ concentration increases then the equilibrium position moves right. this eases reduction so the standard electrode potential gets more positive
whats the difference between the overall reaction of an electrochemical cell and its recharged reaction
the recharging reaction is the overall reaction in reverse (normal: Cu^2+ + 2Fe^2+ –> Cu + 2Fe^3+ recharging: Cu + 2Fe ^3+ –> Cu^2+ + 2Fe^2+)
why do fuel cells not need recharging
they are continually supplied with new fuel and oxygen so the concentrations don’t decrease. this also maintains a constant voltage
advantages of fuel cells
less pollution more efficient
how to optimise fuel cells
increase temperature for a faster reaction however, fuel cells are exothermic so high pressures counteract this or use catalysts
whats the overall reaction equation of a fuel cell
its the same as the complete combustion reaction of the fuel used
hydrogen or ethanol fuel cells? (advantages/disadvantage of each)
hydrogen: readily available but safety of storage issues new fuel stations needed as its gaseous Ethanol: made from renewable resources abundant raw materials to make it easier to store than hydrogen no new fuel stations needed as its liquid