Electrochem

Question 1

what is oxidation

Answer 1

losing an electron to increase the oxidation number

Question 2

what is the oxidizing agent

Answer 2

the chemical substance taking away/gaining the electron
= is reduced

Question 3

what is reduction

Answer 3

gaining an electron to decrease the oxidation number

Question 4

what is the reducing agent

Answer 4

the chemical substance that donates electrons/loses in reduction
= is oxidized

Question 5

what is an anode

Answer 5

the electrode in electrochemical cells at which oxidation occurs

Question 6

what is a cathode

Answer 6

the part of electrochemical cells at which reduction occurs

Question 7

what are galvanic cells

Answer 7

generate electricity if REDOX reaction is spontaneous

Question 8

what are voltaic cells

Answer 8

galvanic cells

Question 9

what are elctrolytic cells

Answer 9

reaction is forced to happen using electricity id reaction is non spontaneous

Question 10

what is disproportionation

Answer 10

a self-redox reaction where the same substance is both oxidized and reduced

Question 11

what is comproportionation

Answer 11

two substances are oxidized and reduced to form 1 product with an intermediate oxidation #

Question 12

what is the standard hydrogen electrode

Answer 12

the reference that all other electrodes are measured against

Question 13

what is the standard electrode potential

Answer 13

E°SHE = 0V

Question 14

what is standard cell potential

Answer 14

E°cell = the potential difference/voltage of a cell formed from 2 standard electrodes

Question 15

what does a positive E° mean

Answer 15

electrons flow from SHE to electrode = reduction
-spontaneous
-cathodic

Question 16

waht does a negative E° mean

Answer 16

electrons flow from electrode to SHE = oxidation
- spontaneous
- cathodic

Question 17

in which direction do electrons flow spontaneously

Answer 17

from higher to lower potential
- ie towards less negative potential

Question 18

when is a cell doing electrical work

Answer 18

in voltaic cells

Question 19

what is electron flow in batteries

Answer 19

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

Question 20

what are primary cell batteries

Answer 20

the cell reaction is not reversible and not rechargeable
- Leclanche (dry) cells and water-activated reserve batteries

Question 21

leclanche dry cells

Answer 21

alkaline batteries that have been adapted to modern dry cells

Question 22

pros and cons of leclanche cells

Answer 22

pros: simple, easy to access, small
cons: gradual self decay -> KOH leak = corrosive, not rechargeable

Question 23

water-activated reserve batteries

Answer 23

designed to produce no voltage until an electrolyte is added
- the anode and cathode are separated

Question 24

pros/cons of water activated reserve batteries

Answer 24

pros: long term storage, delivers high power in short time
cons: limited use and not rechargeable

Question 25

Secondary cell batteries

Answer 25

cell reaction can be reversed by passing electricity through the cell = chargeable - lead acid batteries, nickel-cadmium rechargeable batteries, lithium ion batteries

Question 26

lead acid batteries

Answer 26

when discharging, the reaction is spontaneous, when charging, the cathodes and anodes switch and is then non spontaneous

Question 27

pros and cons of lead acid batteries

Answer 27

pros: supplies a large current and is easily recharged cons: low temperature issues, and toxic lead presence

Question 28

nickel cadmium rechargeable batteries

Answer 28

spontaneous discharge and non spontaneous charge

Question 29

pros/cons of nickel cadmium batteries

Answer 29

pros: less expensive than alkaline, rechargeable, low self discharge cons: banned in europe for cadmium = highly toxic

Question 30

Lithium ion batteries

Answer 30

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

Question 31

pros of lithium ion batteries

Answer 31

faster charge,lasts longer, higher power density

Question 32

Fuel cells

Answer 32

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

Question 33

what is corrosion

Answer 33

the degradation of metals by a naturally occurring electrochemical process = unwanted voltaic/galvanic reactivity

Question 34

what happens in corrosion

Answer 34

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

Question 35

how to protect against corrosion

Answer 35

prevent oxygen contact using electrochemistry and seective coatings or apply cathodic protection

Question 36

what is cathodic protection

Answer 36

when a more active metal (sacrificial anode) is attached to the metal to protect it from corrosion by being preferentially oxidized instead

Question 37

what is electrolysis

Answer 37

the process of applying electrical energy to force an nonspontaneous electrochemical reaction to occur - used in electroextacting, electroplating and recharging cells

Question 38

what are factors contolling electrolysis

Answer 38

1. often need to use excess voltage to forge the reaction with an overpotential 2. overpotential can result in competing reactions, especially since reactants aren't in standard state 3. the electrode choice: to avoide unwanted redox, inert passive electrodes are used, which ensures that only chemicals in the electrolyte solution react

Question 39

what is the chloralkali process

Answer 39

industrial electrolysis of NaCl to produce Cl2 gas, which is too reactive to exist in nature - used for chem warfare in ww1