electrochemical cells Flashcards
what is a voltaic cell?
a type of electrochemical cell which converts chemical energy into electrical energy
what is a half cell?
a cell which contains the chemical species present in a redox half equation
how is a voltaic cell made?
the connection of two half cells, allowing electrons to flow
why must the chemicals be kept apart in a voltaic cell?
if allowed to mix, electrons would flow in an uncontrolled way and heat energy would be released instead of electrical energy
how is a metal half cell made?
metal rod dipped in solution of its aq metal ioon
describe the electron flow in a half cell compared to an electrochemical cell
half cell = no net transfer of electrons in/out of metal
electrochemical = direction of electron flow depends upon relative tendency of each electrode to release electrons
what is an ion half cell?
contains ions of same element in different oxidation state
eg iron II and iron III ions
how is an ion half cell made?
as there is no metal to transport electrons, an inert metal electrode made of platinum is in solution
- allows electrons in/out of cell
which is the negative electrode?
the electrode with more reactive metal
- loses electrons
- is oxidised
which is the positive electrode?
the electrode with the less reactive metal
- gains electrons
- is reduced
define ‘standard electrode potential’
the tendency for a species to be reduced and gain electrons
describe what is meant by standard electrode potential?
electrode multi force of a half cell connected to a standard hydrogen half cell under standard conditions
what is the standard electrode potential of hydrogen?
0 V
describe how a standard electrode potential measured
connect half cell to standard electrode
connect 2 electrodes by a wire to allow flow of electrons
connect solutions with a salt bridge (allows more ions to flow)
describe the salt bridge
allows ions to flow
contains concentrated solution of electrolyte that doesn’t react with either solution
eg filter paper soaked in KNO3 aq
what does a more negative standard electrode potential tell us?
greater tendency to lose electrons: undergoes oxidation
less likely to gain electrons and undergo reduction
what does a more positive standard electrode potential tell us?
greater tendency to gain electrons: undergoes reduction
less likely to lose electrons and undergo oxidation
what standard electrode potential do metals usually have?
negative
- loss of electrons
- oxidation
what is the relationship between reactivity and standard electrode potential?
more negative = more reactive in losing electrons
more positive = more reactive in gaining electrons
describe how you would set up cells to measure cell potentials
prepare 2 standard half cells
- metal: must be 1moldm-3
- ion: both metal ions must have same conc, must be an inert electrode
- gases: gas must be 100kPa, solution conc 1moldm-3, inert electrode
connect metal electrodes of half cells to voltmeter using wires
add a salt bridge & connect the solutions
record standard cell potential from voltmeter
how is standard cell potential calculated from standard electrode potentials?
electrode potential of positive electrode - electrode potential of negative electrode
in an electrochemical cell, what are the charge carriers in the wire & salt bridge?
wire = electrons
salt bridge = ions
state the standard conditions used for electrochemical cells
gas pressure → 100kPa
temperature → 298 K/25°C
concentration → 1 mol dm⁻³
