commercial cells

overall eqns given for completeness but can be deduced

give the features of non rechargeable cells and explain why they are necessary:

• porous separator - allows ions to move/flow/transfer

• carbon rod - made from graphite to allow e^- to flow

• zinc - container for cell (gets used up)

give an example of a non rechargeable cell:

either:

• alkaline battery

• dry cell

suggest why a non rechargeable cell often leaks after being used for a long time (1)

Zn oxidised

give an example of a rechargeable cell and give the 2 ½ eqns associated w/ it:

lithium ion:

• Li⁺ + CoO₂ + e^- ⇌ LiCoO₂ (+ve electrode)

• Li⁺ + e^- ⇌ Li (-ve electrode) 

give the overall eqn for the reaction that occurs in a lithium-ion cell:

Li + CoO₂ ⇌ LiCoO₂

for a rechargeable reaction, what do the different directions of the reaction apply to?

• forward reaction = discharge (being used)

• backward reaction = recharge (being charged)

give the 3 types of cell:

• non rechargeable (irreversible)

• rechargeable (reversible)

• fuel cells

describe how an alkaline hydrogen-oxygen fuel cell works:

• H₂ and O₂ gases are supplied to separate platinum-containing electrodes

• an anion-exchange membrane separates the electrodes, allowing passage of anions (OH^-) and water but not the gaseous reactants

• the electrolyte is an aq KOH soln

• e^- flow from the -ve electrode through an external circuit to the +ve electrode, while OH^- ions migrate through the anion-exchange membrane towards the -ve electrode

give the eqn for the reaction at the -ve electrode of an alkaline hydrogen-oxygen fuel cell:

H_{2 (g)} + 2OH^- _(aq) → 2H₂O _(l) + 2e^-

give the eqn for the reaction at the +ve electrode of an alkaline hydrogen-oxygen fuel cell:

O_{2 (g)} + 2H₂O _(l) + 4e^- → 4OH^- _(aq)

give the overall eqn for the reaction that occurs in an alkaline hydrogen-oxygen fuel cell:

2H₂ + O₂ → H₂O

give a benefit of using non-rechargeable cells:

cheap

give a drawback of using non-rechargeable cells:

difficult to dispose of/waste issues

give 3 benefits of using rechargeable cells:

• less waste as metal compounds reused

• cheaper in the long run

• lower environmental impact

give 2 drawbacks of using rechargeable cells:

• need E source to recharge

• some waste at end of useful life

give 3 benefits of using hydrogen fuel cells:

• converts more of the available E from combustion of H₂ into KE of car

• no pollutants (CO₂, SO₂ etc.) as only waste product is H₂O

• efficient

• no need to recharge

give 4 drawbacks of using hydrogen fuel cells:

• need constant fuel supply

• H₂ is flammable and explosive

• high cost

• difficult to source H₂ (usually made using fossil fuels)

suggest why the recharging of a lithium cell may lead to the release of CO₂ into the atmosphere (1)

electricity from recharging the cell may come from power stations burning fossil fuel