Using & Controlling Reactions: Electrochemistry

Question 1

Electrochemical Cell

Answer 1

• two electrodes (anode & cathode) connected by metal wire
• electrolyte (molten ionic compound/aqueous solution with free ions)
• oxidising agent at cathode (RC), reducing agent at anode (AO)

Question 2

Galvanic cell

Answer 2

• portable source of electric current (battery)
• chemical energy -> electrical energy
• spontaneous redox reaction
• anode = more active metal, -ve charge as electrons are generated here
• cathode = less active metal, +ve charge as electrons are consumed at cathode

Question 3

Electrolytic cell

Answer 3

• used in the production of active metals (Gp I & II)
• electrical energy -> chemical energy
• non-spontaneous redox reaction
• electrolysis of molten halides (halogen ions) & inert carbon electrodes
• anode = +ve as electrons are drawn away
• cathode = -ve as electrons are pushed toward it
• used for industrial production of lithium, potassium, lead, sodium, barium, strontium`

Question 4

Redox Half Equations

Answer 4

1. balance any elements other than O or H
2. balance O with H2O
3. balance H with H+
4. balance charges with electrons

Question 5

Fuel cells

Answer 5

= Galvanic cells in which the electrode reactants are in continuous supply
- gaseous fuels fed continuously to an anode compartment & oxident (eg. oxygen) fed continuously to cathode compartment

Question 6

Advantages of Fuel Cells

Answer 6

• continuously produce electric current (with continuous supply)
• high operating efficiency
• use readily available fuel & oxidants
• electrodes & electrolytes not consumed
• require minimum maintenance
• do not produce pollutant gases eg. sulfur dioxide, oxides of nitrogen

Question 7

Rechargeable Galvanic cells

Answer 7

• external electrical supply can reverse electrode reactions and recharge Galvanic cell
• during DISCHARGE
  … electrode reactions produce electric current
  … oxidiser & reducer are used up
• during RECHARGE
  … external power source provides electric current to electrodes
  …discharge reactions reverse, original oxidiser & reducer are regenerated
  … becomes electrolytic cell