electrode potentias. Flashcards
pt What is a half cell?
= one half of an eletrochemical cell
= metal dipped into its ions
= platinum electrode with 2 aqeous ions
= electrocgemical cell is joining 2 half cells
What do we use for the electrode with 2 aqeous ions?
= inert but electrically conductive electrode
=platinum
=
What is an electrochemical cell made from?
= 2half cells- one is undergoing reduction the other oxidation
= wire
= voltmeter
= salt bridge
What is the movement of electrons?
= electrons move from a more reavtive metal to a less reactive
WHat happens with the oxidation side?
= the metal ion is produced, the electrode becomes thinner as more ion is produced to make electrions
= oxidation is the loss of electrons
What happens in the reduction side?
= the metal ion gains electrons to form the metal
What is the salt bridge?
= KNO3
= filter paper dipped in solution, ions flow through to balance the charge in the ionic substance
= complete the circuit
What is electrode potential:?
= measured in volts
= tells us how easily the half cells gives up electrons, oxidised
= the half cells have reversible reactions
= the forwqards reaction is the reduced form
What is the cathode and what is the anode?
= the more negative is the andode- this is oxidised, and on the , the more positibe is the cathode, this is reduced and on the rhs
In the electrochemical series what happens as we go up?
= stronger reducing agent as we go up, with descending values
= agents on left are more easilt reduced, so are a better oxidising agent
=
In the electrochemical series what happens if we go down?
= stronger reducing agent as we go down, if the values are descending
= agents on the right are moe reasily oxidised,
How do we calculate the standard cell potential?
RHS-LHS
= rhs is the agent getting reduced, and lhs is the agent getting oxidised
rhs-lhs
What are cell notations?
= draw set up of cell
= standard way of presenting cells
= negative goes on left (anode) and cathode goes on rigt positive
= reduced form l oxidised form l oxidised l reduced
= double lines show the salt bridge
What happens if you two have aqeous ions?
= write bith oxidisisng states, wigh comma, and platinum when using 2 non metals
How do we predict feasability?
= identify the cathode and anode- whether which one is oxidised and reduced
= oxidised equation is reversed
= combind the equations
= calculate the ecell, all feasible reactions this will be positive
What are batteries?
= electrochemical cells, that come in 2 main forms, rechargable and nonrechargable
what are non rechargable batteris + key points?
= tend to be cheaper
= reversible, last longer and cheaper in long term
e.g lithium ion batteries
= metals can be reused
What is the electrolyte?
= part of the batery that acts as a conductive pathway for ions, to move from one electrode to the other
How do rechargable batteries work?
= plugging them into supply a current
= current forces electrons, to flow in opposite direction
= reverse the discharge equation to show battery recharging
What are fuel cells?
= electricity is generated, by a continious external supply of chemicals rather than ready store in batteries
= a fuel cell uses energy, from the reaction of a fuel with oxygen to create a voltage
For the lithium nattery what are the details?
= Li + CoO2 => Li+[CoO2]-
= Li | Li+ ||Li+, CoO2 |Pt
= reagants in the cell are absorbed, onto powdered graphite, that acts as a support medium
= allows ions to react in the absence of a solvent, such a water
= water would not be a good solvent, react with metal
What is the overall equation for a hydrogen fuel cell?
= 2H2 + O2 => 2H2O
Why will fuel cells maintain a constant voltage?
= over time maintain a constant voltage
= contionously fed with fresh H2 and O2 so maintaining a constant concentration, of reactants
= differs from ordinary cells, where voltaged drops as reactant concentration drops
What conditions do we use for this?
= rate is too slow originally
= high temperature are used, to increase rate of reaction, a higher pressure is used to counteract the fact that e cell falls
What are the advantages of fuel cells?
= less pollution
= less co2
= greater effieincy
What are the limitation of hydrogen fuel cells?
= expensive- Hydrogen is readily available by the
electrolysis of water, but this is expensive
= storing and transporting hydrogen,
= limited lifetime0 require replacements, and hih production costs
= use of toxic chemicals in production
= hydrogen is explosibe
What is the standard hydrogen electrode?
= potentials of all cells are measured by comparing their potential to this
= all reactions must be in standard conditions and states
What is the hydrogen electrode equalibrian>?
= H2 => 2H+ + 2e-
= pt| H2| H+
=
What conditions are needed?
= hydrogen gas at 100kpa
= solution conaining hydrogen ions 1 mol dm^-3 or hcl
= 298k
= platinum electrode
=
What are secondary standards?
= often a different standard is used
WHat will colbalt change to?
= +4 to +3
What are the equations for lithium ion cell, reduction?
Li+ + CoO2 +e- => Li+[CoO2]-
What is the equation for the lithium ion cell, oxidation?
= Li+ + e- => Li
What is the advantage of ethanol fuel cells?
= ethanol can be made from renewable sources-carbon nuetral
= raw materials to produce ethanol, by fermination are abundant
= less explosive compared to hydrogen,
What is an electrochemical series?
= list of electrode potentials in numerical order
Why may emf values be different?
= may not be in standard conditions
why may a cell leak?
= has reacted, may be oxidised
What are the advantages of ethanol fuel cells?
= ethanol can be made from renewable sources, (glucose fermentation), carbon nuetral
= ethanol is less explosive, easier to store than hydrogen
=
What happens at tge oxygen electrode?
4e- + 4H+ + O2 => 2H2O
What happens at the ethanol electrode?
= C2H4OH + 3H2o => 2CO2 + 12H+ + 12e-
What is the overall equation?
= c2H5OH + 3O2 => 2Co2 + 3H2o
What happens to oxygen equation?
= o2 + 4H+ + 4e- => 2H2O
why is ethanol carbon nuetral?
= when ethanol is in fermentation, produces co2 and this is used in photosynthesis.
For an alkaline hydrogen fuel cell what is the equation for notion?
= Pt|H2(g)|OH–
(aq),H2O(l)||O2(g)|H2O(l),OH–
(aq)|Pt
What is an disadvntage of a fuel cell?
= fossil fuels are used, this contributes to co2 emissions,
What is an advantage?
= more efficient than combustion engines
= more energ is turned into kinetic energy, o bsution engines wasdte a lot more as thermal energy
