Unit 3.1 - Redox and standard electrode potential (physicsandmathstutor))
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define oxidation in terms of electron transfer
loss of electrons
define reduction in terms of electron transfer
gain of electrons
what is a redox reaction
a reaction in which oxidation and reduction occur on different species simultaneously
what is standard electrode potential
the potential across electrons when a redox system is connected to a hydrogen half-cell (under standard conditions)
what are conditions required for measuring standard electrode potential
• 298K temperature • 100kPa pressure • 1.00mol/dm3 conc of ions
why must metal electrodes be cleaned with sandpaper before creation of an electrochemical cess
to remove any metal oxide that has formed on the surface + improve conductivity
describe movement of electrons in an electrochemical cell
electrons flow through the wire from + to - electrode
why is a salt bridge used in an electrochemical cell
-maintain charge balance and complete the circuit
why must salt be inert in the salt bridge
salt must be inert so that it doesn’t react with solutions (cell potential would change if reactive salt was used)
what moves across salt bridge
ions
what rance of cell potential values is a process feasible
cell potential must be greater than 0
how is cell potential calculated
(+)-(-)
why might theoretical cell potential values be different to values obtained experimentally
conditions may be non-standard
in an electrochemical cell, is the more negative half cell oxidised or reduced
oxidised
what is a fuel cell
a cell that continually produces a voltage as long as it is supplied with oxygen and a fuel (like hydrogen)
what is the only product of a hydrogen-oxygen fuel cell
water
how does a hydrogen-oxygen fuel cell work
• hydrogen and oxygen are pumped through porous electrodes. The electrolyte is often an acid (phosphoric acid) • hydrogen and oxygen react = energy + water
what are the 2 half equations taking place in hydrogen-oxygen fuel cell
2H₂ + 4OH⁻ <–> 4H₂O + 4e⁻ O₂ + 2H₂O + 4e⁻ <–> 4OH⁻
write an overall reaction that takes place in a hydrogen-oxygen fuel cell
2H₂ + O₂ –> 2H₂O
3 advantages of using fuel cells
• no pollution • produce more energy than alternative fuel (like petrol) • process is continuous as long as fuel is supplied
4 disadvantages of using fuel cells:
• expensive materials • hydrogen is hard to store • efficiency effected by temp • high pressure tanks needed