unit 4 section 3 electrode potentials and cells Flashcards
describe an electrochemical cell
two different metals are dipped in salt solutions of their own ions and is connected by a wire. there is also a salt bridge which allows the free flow of electrons from one cell to another.
explain the movement of electrons in an electrochemical reaction
the electrons flow the wire from the more reactive metal to the least reactive metal.
what is the cell potential or the EMF
it is the difference between the voltages of the two half cells.
the voltages can be measured with a voltmeter in the external circuit
what is electrode potentials
it is the measure of how easily a metal is oxidised
- metal that is easily oxidised has a more negative electrode potentials
- while metals that are harder to oxidise will have a less negative or more positive electrode potential.
what is the conventional representation and how it is done
it is the shorthand way of drawing/representing electrochemical cells.
- the oxidised forms and the reduced forms of each species of each half-cell and then arrange them in a row.
Zn | Zn2+ || Cu2+ | Cu
the || represents the salt bridge
what is the equation for the electrode potential
E(cell) = E(right hand side) - E(left hand side)
or
E(cell) = E(reduced) -E(oxidised)
what factors affect the electrode potential
since the half cell reaction is reversible, factors such as concentration, temperature and pressure affects the position of the equilibrium which affects the electrode potential.
how can the factors that affect the electrode potential be overcome
they use standard conditions . this means you always getting the same value for the electrode potential and you can compare values for different cells.
what is the standard hydrogen electrode
it is used as a reference to measure the standard electrode potentials. in the standard hydrogen electrode, hydrogen gas is bubbled through a solution of aqueous H+ ions.
what is an electrochemical series
it is a big list of electrode potential for different electrochemical half-cells
what is the equation for the electrode potential when you are given the electrochemical series
E(cell) = E(reduced) - E(oxidised)
what type of reactions occurs in a non rechargeable battery and what is the common type of cell
they use irreversible reactions, a common type of non rechargeable cell is a dry alkaline battery.
what types of reaction does rechargeable batteries use
they use reversible reactions
what are the two types of rechargeable reaction
NiCad( nickel-cadmium ) and lead-acid.
explain how a rechargeable batteries work
to recharge the batteries, a current is supplied to force electrons to flow in the opposite direction around the circuit and reverse the reactions. this is possible because none of the substances in the rechargeable reaction are used up or lost.
what is the difference between fuel cells and electrochemical
in a fuel cell the chemicals are stored separately outside of the cell and is fed in when electricity is needed.
in a electrochemical cell the chemicals are not outside of the cell.
what are the pros of using fuel cells
-fuel cells are more efficient than the combustion - they convert more of their available energy into kinetic energy to get the car moving.
-only waste product is water
- doesn’t need to be recharged, just needs to be supplied with hydrogen & oxygen.
what are the cons of fuel cells
-need energy to produce hydrogen, this is done through the electrolysis of water, this requires energy which is mainly gathered by fossil fuels.
what is a half cell
it is one half of an elecrochemical cell.
- they can be made of a metal dipped in its ions, or a platinum electrode with two aqueous ions
why do they use platinum as an electrode if the ion does not have a solid metal form
this is because platinum is is inert and will not react with the ions. also the platinum can conduct electricity.
what must the salt bridge do in order for the cell to work
the salt bridge must not touch the electrodes and the salt bridge must make contact with the solutions of ions.
what is an acromym for how to know what the electrode potentials mean
NO PROBLEM
- the more Negative value means it is being Oxidised
- the Positive value ( or less negative value) is being Reduced.
E(cell) = E(reduced) - E (oxidised)
what is the electrode potential of the standard hydrogen electrode
0.00V
what are the standard conditions for the standard hydrogen potentials
298k
100kpa
1 mol dm-3
what do all feasible reaction have
they all have a positive Eθ
