AC11: Electrochemistry Flashcards
Describe the setup of an electrochemical cell
two half cells, containing aqueous ionic solution, metal electrode, and the two electrodes connected via a voltmeter, the two solutions connected via a salt bridge
what is the purpose of the salt bridge in an electrochemical cell
to complete the circuit
Define the term standard electrode potential
the voltage measured when a half-cell is connected to a standard hydrogen half-cell, at standard conditions of 298K, 100kPa, 1.00 moldm-3 for all solutions
Explain the purpose of the salt bridge, and state how a simple salt bridge may be constructed
the salt bridge completes the electrical circuit by connecting the 2 half cells to allow the flow of ions
salt bridge can be made from soaking a porous material with a saturated solution of KNO3 (aq)
Describe how to set up a standard hydrogen half-cell
beaker containing H+ ions (1.00 moldm-3)
Pt (s) electrode
H2 gas being pumped in at 100kPa
298K temperature
What is the difference between electrode potentials and cell potentials
electrode potential is of the singular half cell whereas cell potential is the combination of different half-cell electrode potentials
How do you work out the cell potential of a combination of half-cells
standard electrode potential of more positive half-cell minus standard electrode potential of less positive half-cell
Would the more positive standard electrode potential be for the half-cell that favours reduction or oxidation
reduction
Would the less positive standard electrode potential be for the half-cell that favours reduction or oxidation
oxidation
State and explain 2 limitation of using standard electrode potentials for predicting feasibility
1- if conditions are not standard, then the value of E will differ from E (standard)
2- If the activation energy of the reaction is high and so the rate of reaction is very low, we may not see a reaction
State the 2 types of storage cells
non-rechargeable
rechargeable
Describe is a key feature of storage cells
they are closed systems meaning no more reactants can be added and no more waste products are removed
How do you denote a non-rechargeable and rechargeable cell
non-rechargeable cells are primary cells
rechargeable cells are secondary cells
What is the key difference between primary/non-rechargeable and secondary cells /rechargeable cells
primary/non-rechargeable cells have redox reactions occurring in them to generate are voltage, these redox reactions result in an overall reaction which is IRREVERSIBLE whereas secondary cells /rechargeable cells have redox reactions occurring in them that ARE REVERSIBLE by ‘charging’ and so can regenerate the original reactants
Give 4 examples of secondary/rechargeable cells
lead-acid batteries
nickel-cadmium
nickel metal hydride
lithium ion and lithium polymer ion
Describe and explain how fuel cells work
They use a redox reaction of a fuel with oxygen/oxidant to generate a voltage
reactants (fuel and oxidant) are continuously introduced to the cell and waste product flow out - open system
Describe and explain the set up of a fuel cell
2 Pt (s) electrodes connected to each other (by wires running through a ⊗) with electrons flowing from one electrode to the other electrode. A fuel (e.g. H2) is introduced to the cell which oxidises, giving its electrons to the Pt electrode, and forming 2H+ (unused H2 and H2O leaves the cell). 2H+ (protons) move through the electrodes via a Proton Exchange Membrane. O2/air is introduced to the other side of the cell which is reduced by taking in electrons from the 2nd Pt electrode, and becomes H2O (binding with the H+ from the P.E.M. Unused O2 and waste H2O leaves the cell
