Electrochemical cells

Question 1

What do non-rechargable cells use?

Answer 1

irreversible reactions

Question 2

Where are non-rechargable cells found?

Answer 2

in TV remote controls, torches, smoke alarms

Question 3

What do rechargeable cells use?

Answer 3

Reversible reactions

Question 4

Where will you find rechargeable cells?

Answer 4

Mobile phones
Laptops
Cars

Question 5

What are the two half equations in common zinc-carbon dry cell batteries? (non-rechargable)

Answer 5

Zn -> Zn2+ + 2e-

2MnO2 + 2NH4+ + 2e- -> Mn2O3 + 2NH3 + H2O

Question 6

What are the two half equations in lithium cells made up of lithium cobalt oxide electrode and graphite electrode?

Answer 6

Li+ + CoO2 + e- -> Li+[CoO2]-

Li+ + e- -> Li

Question 7

How are batteries recharged?

Answer 7

A current is supplied to force electrons to flow in the opposite direction around the circuit and reverse the reactions

Question 8

Where are chemicals stored in a fuel cell?

Answer 8

They are stored separately outside the cell and fed in when electricity is required

Question 9

Outline how an alkaline hydrogen-oxygen fuel cell can be used to power an electric vehicle.

Answer 9

1) Hydrogen and oxygen gases are fed into two separate platinum-containing electrodes.
2) The electrodes are separated by an anion exchange membrane that allows anions and water to pass through it but stops hydrogen and oxygen from passing though.
3) Hydrogen is fed to the negative electrode
4) The electrons flow from the negative electrode through an external circuit to the positive electrode
5) The OH- ions pass through the anion exchange membrane towards the negative electrode
6) Oxygen is fed to the positive electrode
7) Overall effect is that the hydrogen and oxygen react to make water

Question 10

Why is coating an electrode in a thin layer of platinum better than using a solid platinum rod?

Answer 10

It is cheaper

Provides a larger surface area

Question 11

What are strengths of using fuel cells?

Answer 11

• They are more efficient: convert more of their available energy into kinetic energy to get the car moving
• The waste product is water, no toxic chemicals to dispose of and no CO2 contributing to the greenhouse effect
• Dont need to be recharged like batteries

Question 12

What are limitations of using fuel cells?

Answer 12

• Need energy to produce a supply of hydrogen which can be produced by electrolysis of waste water but this requires electricity generated from fossil fuels
• not carbon neutral
• hydrogen is highly flammable - handled carefully when transported and stored
• refuelling stations are rare at the moment