UNIT 1 Section 9 - Electrode Potentials Flashcards
what is a half cell
one half of an electrochemical cells which is an electrode with its aqueous ions in solution
what is an electrochemical cell
consisting of two half cells, a voltmeter, a salt bridge where one half cell undergoes oxidation and the other half cell undergoes reduction as the electrons flow from a more reactive metal to a less reactive one
what is emf
the potential difference between 2 half cells
what is the electrode potential a measurement of
how easily a half cell gives up electrons and oxidised
how are the equations in the electrochemical series written
the reduced form is written in the forwards reaction
what does a negative and positive electrode potential mean for electrochemical cells and what occurs because of this
The most negative will undergo oxidation (lose)
The most positive undergoes reduction (gain)
what is the standard hydrogen electrode used for
used as a reference to measure standard electrode potential as half cells cant be measured on their own
what are the standard conditions of a hydrogen electrode
- 298K temp
- 100kPa pressure
- 1 moldm-3 concentration of ions
in the equations in the electrochemical series which side are the oxidising agents and which side are the reducing agents and is it the more or less negative
left oxidising agent- most positive
right is reducing agent- most negative
how do you work out the electrode potential of a cell with the electrochemical series
electrode potential of the reduced half cell - electrode potential of the oxidised half cell
outline how we do cell notation
R/O//OR
the lines represent different states but if they are the same state use a comma
the // represents the salt bridge
the most negative half cell goes on the left of the salt bridge
hoe can you predict the feasibility of a reaction using standard electrode potentials
- take the oxidised equation and reverse it so both equations have reduction going in the forwards direction
- combine the equations and that is your feasible reaction
- compare the equation of feasibility with the equation given in the question and see if they match are it is feasible
- to check if the electrode potential of the equation in the questions is positive it is feasible
what is a battery
electrochemical cell
name a rechargeable cell and what is the strcuture of it
lithium ion battery
- has lithium colbalt oxides and grephite electrodes with an electrolyte of lithium salt dissolved in an inorganic solvent
what is the role of an electrolyte in a battery
acts as a conductive pathway for ions to move from one electrode to another
how do rechargeable electrons charge
plugging them into a supply of current and this forces the electrons to flow in the opposite way and therefore reverses the overall discharge equation
what is different about fuel cells and batteries
fuel cells need a continuous external supply of chemicals rather than a ready store like batteries and the supply is external
outline the advantages of fuel cells
+ more efficient
+ more energy is converted into kinetic energy and less waste on thermal energy
+ don’t need to recharge them
+ only waste product is water
outline the disadvantages of fuel cells
- hydrogen is highly flammable and must be stored and transported correctly making it expensive and it has to be transported in pressurised containers
- energy is required to make the hydrogen and oxygen used and that normally comes from hydrolysis which uses fossil fuels
how does a fuel cell work
- hydrogen is fed into the cell and reacts with the OH- ions to form water and 4 e-
- the electrons then go to the platinum electrode and are used to power something
- oxygen is fed in on the other side and reacts with the water and 4 e- to produce OH- ions again
- the electrons flow to the negative electrode which is also made from platinum
- the electrolyte made from the KOH carry the OH- ions formed from the cathode to the anode
- water is eliminated by being released into the surroundings as gas
