electrochemical cells Flashcards
how is a potential difference produced?
by the flow of electrons between electrodes in the cell
what do electrochemical cells consist of?
two solutions with metal electrodes and a salt bridge
what does the salt bridge consist of and why?
unreactive ions so they can move between the solutions and carry the charge, but not interfere with the reactions
what half cell goes on the right?
the reduction – the most positive
what half cell goes on the left?
the oxidation – the most negativewh
what species go closest to the salt bridge?
the most oxidised species
how is the salt bridge represented?
two double vertical lines
what is the potential difference or the standard hydrogen electrode?
0.00V
what are the standard conditions of the standard hydrogen electrode?
298k temperature
1.00 mol dm-3 concentration of ion solutions
100kPa pressure
what is the electrode usually made of if there is no electrode already present?
platinum
what does a negative potential difference show?
the species are the best REDUCING AGENTS so are easily oxidised
the species will lose electrons
what does a positive potential difference show?
the species are the best OXIDISING AGENTS so are easily reduced
the species will gain electrons
how do you calculate a cells emf?
emf = Eright - Eleft
what will increasing the concentration of the solutions do to the cell emf?
make it more positive as fewer electrons are produced in the reaction
what will increasing the pressure do to the cells emf?
make it more negative as more electrons are produced
what is an example of a rechargable battery?
lithium ion cells
what does a lithium ion cell consist of?
lithium cobalt oxide electrode and a graphite electrode
what can a salt bridge be?
- a piece of filter paper soaked in a solution of unreactive ions
- a tube containing unreactive ions in an agar gel
why is a high resistance voltmeter used?
so there is no current
what electrode is the anode?
the most negative
where the oxidation occurs
what electrode is the cathode?
the most positive
where the reduction occurs
what is the electochemical series?
a list of electrode potentials in numerical order
what are the examples of non-rechargable cells?
zinc-carbon
alkaline
what are the examples of rechargeable cells?
lithium ion
lead-acid
nickel-cadmium
what is the reduction equation in the lithium ion cell?
Li+ + CoO2 + e- –> LiCoO2
what is the oxidation equation in the lithium ion cell?
Li –> Li+ + e-
why don’t fuel cells run out?
they have a constant supply of chemicals to the cell
what is the most common type of fuel cell?
hydrogen-oxygen fuel cell
how does a hydrogen-oxygen fuel cell work?
anode - hydrogen is oxidised
electrons move between electrodes via an external wire
cathode - oxygen is reduced to water
benefits of using re-chargeable cells?
less waste , cheaper in the long run , low environmental impact
benefits of hydrogen fuel cell?
only waste product is water , don’t need recharging , very efficient
risks of re-chargeable cells?
some waste issues at the end of its life
risks of hydrogen fuel cells?
need constant supply of fuels , hydrogen is flammable and explosive
explain how a salt bridge provides an electrical connection between the two solutions?
allows ions to flow between the solutions
