C7.5 Fuel Cells Flashcards

1
Q

what is a fuel cell?

A

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

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2
Q

How do hydrogen fuel cells work?

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

HYDROGEN + OXYGEN –> WATER

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3
Q

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

A

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
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4
Q

why do electrons flow from most reactive to least?

A

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

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5
Q

The greater the difference in reactivity…

A

the higher the voltage produced

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6
Q

difference between normal cells, rechargeable cells and fuel cells?

A

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

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7
Q

what factors affect the voltage produced ?

A
  • greater difference in reactivity
  • concentration of electrolyte
  • type of electrolyte
  • type of electrode
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8
Q

ADVANTAGES OF HYDROGEN FUEL CELLS

A

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

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9
Q

DISADVANTAGES OF HYDROGEN FUEL CELLS

A

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

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10
Q

how does the recharging process of cells occur ? 4mks

A
  • chemical reaction is reversible
    when external current is applied
  • so product ca turn back into reactants
  • hence movement of electrons continue to take place
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11
Q

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

A

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

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12
Q

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

A

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

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