hydrogen fuel cells

Question 1

What happens the emf of a chemical cell (battery) over time?

Explain why

Answer 1

decreases

reactants gets used up (reach equilibrium)

Question 2

What happens to an electrochemical reaction when a cell is recharged

Answer 2

it is reversed

Question 3

Write an equation for the reaction of hydrogen with oxygen

Answer 3

H2 + ½O2 ⎯→ H2O

Question 4

Explain the environmental advantage of using hydrogen as a fuel

Answer 4

produces only H2O vapour – not greenhouse gas emissions

Question 5

what are the Advantages and disadvantages of hydrogen fuel cells

Answer 5

Advantages

constant emf as new reactants are produced

works at room temperature so low thermal energy loss (compare to burning hydrogen)

produces H2O as by-product, no greenhouse emissions or other pollutants such as NOx, SO2 (be specific)

Disadvantages

little hydrogen infrastructure in place (petrol stations)

production of H2 currently energy intensive (produces greenhouse gases in power stations)

storage of hydrogen is difficult and dangerous (explosive gas)

Question 6

Deduce half equations for a hydrogen-oxygen fuel cell operating in alkaline conditions

Use these half equations to explain how an electric current can be generated

Answer 6

+ electrode
O2 + 2H2O + 4e- → 4OH-

• electrode
  H2 + 2OH- → 2H2O + 2e-

hydrogen electrode produces electrons

oxygen electrode accepts electrons

Question 7

Explain why a fuel cell does not need to be recharged

Answer 7

hydrogen (fuel) is continuously supplied/fed in

Question 8

To provide energy for a vehicle, hydrogen can be used either in a fuel cell or in an internal combustion engine. Suggest the main advantage of using hydrogen in a fuel cell rather than in an internal combustion engine

Answer 8

greater proportion of energy is available from hydrogen-oxygen reaction, less energy wasted as thermal energy

Question 9

Identify one major hazard associated with the use of a hydrogen–oxygen fuel cell in a vehicle

Answer 9

hydrogen is flammable/explosive

Question 10

where does the most negative electrode go

Answer 10

the left

has most negative electrode potential

Question 11

how do you calculate cell emf

Answer 11

right - left

Question 12

Fe3+ + e- → Fe2+ - 0.77 V
Cu2+ + 2e- → Cu + 0.34 V

Identify the negative electrode in the half equation above

Answer 12

Fe3+ + e- → Fe2+