C7.5 Fuel Cells

Question 1

what is a fuel cell?

Answer 1

an electrochemical cell in which a fuel donates electrons at one electrode and oxygens GAINS ELECTRONS at the other electrode

Question 2

How do hydrogen fuel cells work?

Answer 2

• hydrogen fuel provides a source of ELECTRONS, setting up a voltage
  -when hydrogen fuel enters the cell, it becomes OXIDISED

HYDROGEN + OXYGEN –> WATER

Question 3

Example of how a chemical cell/battery works using zinc and copper electrodes

Answer 3

you can use the DIFFERENCE IN REACTIVITY to make cells/batteries

• electrons flow from MOST REACTIVE (zinc) to LEAST(copper)
  -2 metals join together by a wire and put into ELECTROLYTE - electrons will flow from zinc to copper

Question 4

why do electrons flow from most reactive to least?

Answer 4

more reactive metals have a greater tendency too give away electrons / form positive ions

Question 5

The greater the difference in reactivity…

Answer 5

the higher the voltage produced

Question 6

difference between normal cells, rechargeable cells and fuel cells?

Answer 6

Normal cell - goes flat as chemicals are used up
fuel cells- chemicals pumped in to replace those used up
rechargeable cells - when recharging, chemical reactions are reversed to REPRODUCE chemicals used up

Question 7

what factors affect the voltage produced ?

Answer 7

• greater difference in reactivity
• concentration of electrolyte
• type of electrolyte
• type of electrode

Question 8

ADVANTAGES OF HYDROGEN FUEL CELLS

Answer 8

1) no pollution
2) produce more energy per kg than petrol
3) continuous process until fuel stops being supplied

Question 9

DISADVANTAGES OF HYDROGEN FUEL CELLS

Answer 9

1) hydrogen is expensive to produce/store
2) High pressure tanks needed to store , which are dangerous
3) fuel cells affected by low temps - less efficient

Question 10

how does the recharging process of cells occur ? 4mks

Answer 10

• chemical reaction is reversible
  when external current is applied
• so product ca turn back into reactants
• hence movement of electrons continue to take place

Question 11

half equns for reactions at the electrodes in hyrdrogen fuel cell?

Answer 11

H2 –> 2H+ + 2e-
o2 + 4H+ + 4e- –> 2H2O

Question 12

why do non-rechargable cells stop produding electricity/gov example of one?

Answer 12

alkaline batteries
- one of reactants used up - stops chemical reactions
- no flow of electrons so cell stops producing electricty