Chemical Cells and Fuel Cells - Topic 5

Question 1

What does a chemical cell do?

Answer 1

a chemical cell produces a voltage until one of the reactants is used up

Question 2

Fuel cell:

Answer 2

• a fuel cell is a chemical cell that supplied with a fuel (e.g. hydrogen) and oxygen (air) and uses the reaction between them to efficiently release energy
• uses energy from the reaction to generate electricity

Question 3

What happens in a hydrogen-oxygen fuel cell?

Answer 3

hydrogen and oxygen are reacted together and used to produce a voltage and water is the only product

Question 4

Diagram of fuel cell:

Answer 4

Question 5

What are the electrodes made of in a fuel cell?

Answer 5

• conductor
• unreactive metal
• e.g. platinum

Question 6

What leaves the fuel cell?

Answer 6

excess fuel

Question 7

What enters the fuel cell?

Answer 7

• fuel (H2)
• air (O2)

Question 8

What is used as the electrolyte in a fuel cell?

Answer 8

• H+
• acid
• aqueous

Question 9

Half-equation at cathode in a fuel cell:

Answer 9

O₂ + 4H⁺ + 4e⁻ —> H₂O

Question 10

Half-equation at anode in a fuel cell:

Answer 10

H₂ —> 2H⁺ + 2e⁻

Question 11

Strengths of fuel cells:

Answer 11

• only product is H2O - not toxic or a pollutant
• continuous energy, provides sufficient fuel/quick to replace
• high efficiency chemical energy —> electrical energy (no wasted energy)
  
  • more efficient than power stations or batteries
  • no friction or moving parts in fuel cells so no energy lost as heat energy
• can replace batteries which are v. polluting to dispose of as they’re made from highly toxic metal compounds

Question 12

Weaknesses of fuel cells:

Answer 12

• H2 is a gas so takes up far more space to store than liquid fuels like petrol
• H2 gas very explosive making it difficult to store more safely
• expensive to develop and install necessary tech to use fuel cells wifely e.g. safe storage tanks would have to be installed in petrol stations across the country
• H2 often made from either hydrocarbons (which come from fossil fuels) or by electrolysis of water which uses electricity (which is normally generated by burning fossil fuels

Question 13

Advantages of fuel cells over chemical cells:

Answer 13

• once set up, fuel cells require no maintenance - fuel cells operate as long as reactants are supplied
• chemical cells will need to be replaced as they have a limited lifetime - once used up chemical cells cannot be used again or need re-charging
• chemical cells take up space when unused
• voltage drops in chemical cells as reactant are used up whereas voltage is constant in fuel cell as long as hydrogen and oxygen/reactants are supplied
• water produced in fuel cell is only product
• chemical cells contain harmful/toxic substances which need careful disposal after use

Question 14

Disadvantages of fuel cells over chemical cells:

Answer 14

• hydrogen and oxygen must be supplied to fuel cells
• storage of hydrogen difficult as it is a gas - gas tanks take up lot of space as H2 is a gas
• hydrogen is flammable and explosive - dangerous
• fuel cells are expensive to manufacture