Electrochem Flashcards
what is oxidation
losing an electron to increase the oxidation number
what is the oxidizing agent
the chemical substance taking away/gaining the electron
= is reduced
what is reduction
gaining an electron to decrease the oxidation number
what is the reducing agent
the chemical substance that donates electrons/loses in reduction
= is oxidized
what is an anode
the electrode in electrochemical cells at which oxidation occurs
what is a cathode
the part of electrochemical cells at which reduction occurs
what are galvanic cells
generate electricity if REDOX reaction is spontaneous
what are voltaic cells
galvanic cells
what are elctrolytic cells
reaction is forced to happen using electricity id reaction is non spontaneous
what is disproportionation
a self-redox reaction where the same substance is both oxidized and reduced
what is comproportionation
two substances are oxidized and reduced to form 1 product with an intermediate oxidation #
what is the standard hydrogen electrode
the reference that all other electrodes are measured against
what is the standard electrode potential
E°SHE = 0V
what is standard cell potential
E°cell = the potential difference/voltage of a cell formed from 2 standard electrodes
what does a positive E° mean
electrons flow from SHE to electrode = reduction
-spontaneous
-cathodic
waht does a negative E° mean
electrons flow from electrode to SHE = oxidation
- spontaneous
- cathodic
in which direction do electrons flow spontaneously
from higher to lower potential
- ie towards less negative potential
when is a cell doing electrical work
in voltaic cells
what is electron flow in batteries
the electron flows out of the anode/-ve/oxidation side and back into the cathode/+ve/reduction side
-the two sides are separated by an electrolyte
what are primary cell batteries
the cell reaction is not reversible and not rechargeable
- Leclanche (dry) cells and water-activated reserve batteries
leclanche dry cells
alkaline batteries that have been adapted to modern dry cells
pros and cons of leclanche cells
pros: simple, easy to access, small
cons: gradual self decay -> KOH leak = corrosive, not rechargeable
water-activated reserve batteries
designed to produce no voltage until an electrolyte is added
- the anode and cathode are separated
pros/cons of water activated reserve batteries
pros: long term storage, delivers high power in short time
cons: limited use and not rechargeable
Secondary cell batteries
cell reaction can be reversed by passing electricity through the cell = chargeable
- lead acid batteries, nickel-cadmium rechargeable batteries, lithium ion batteries
lead acid batteries
when discharging, the reaction is spontaneous, when charging, the cathodes and anodes switch and is then non spontaneous
pros and cons of lead acid batteries
pros: supplies a large current and is easily recharged
cons: low temperature issues, and toxic lead presence
nickel cadmium rechargeable batteries
spontaneous discharge and non spontaneous charge
pros/cons of nickel cadmium batteries
pros: less expensive than alkaline, rechargeable, low self discharge
cons: banned in europe for cadmium = highly toxic
Lithium ion batteries
lithium ions bind to both electrodes and can flow from 1 terminal to another
on discharge, li+ is released from the carbon-graphite -ve electrode oxidation, migrates, then binds the cobalt oxide +ve electrode in reduction
pros of lithium ion batteries
faster charge,lasts longer, higher power density
Fuel cells
materials pass through the battery, which converts chemical energy to electric energy
- can be run indefinitely when supplied with electrolytes
- new starting materials flow into the cell and are continously replenished
what is corrosion
the degradation of metals by a naturally occurring electrochemical process
= unwanted voltaic/galvanic reactivity
what happens in corrosion
the electron flows downhill from higher to lower potentional spontaneously with a positive E cell
- in damp air, many metals with higher potentials (more negative E°) than oxygen are readily oxidized
how to protect against corrosion
prevent oxygen contact using electrochemistry and seective coatings or apply cathodic protection
what is cathodic protection
when a more active metal (sacrificial anode) is attached to the metal to protect it from corrosion by being preferentially oxidized instead
what is electrolysis
the process of applying electrical energy to force an nonspontaneous electrochemical reaction to occur
- used in electroextacting, electroplating and recharging cells
what are factors contolling electrolysis
- often need to use excess voltage to forge the reaction with an overpotential
- overpotential can result in competing reactions, especially since reactants aren’t in standard state
- the electrode choice: to avoide unwanted redox, inert passive electrodes are used, which ensures that only chemicals in the electrolyte solution react
what is the chloralkali process
industrial electrolysis of NaCl to produce Cl2 gas, which is too reactive to exist in nature
- used for chem warfare in ww1
