hydrogen fuel cells
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What happens the emf of a chemical cell (battery) over time? Explain why
decreases reactants gets used up (reach equilibrium)
What happens to an electrochemical reaction when a cell is recharged
it is reversed
Write an equation for the reaction of hydrogen with oxygen
H2 + ½O2 ⎯→ H2O
Explain the environmental advantage of using hydrogen as a fuel
produces only H2O vapour – not greenhouse gas emissions
what are the Advantages and disadvantages of hydrogen fuel cells
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)
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
+ electrode O2 + 2H2O + 4e- → 4OH- • electrode H2 + 2OH- → 2H2O + 2e- hydrogen electrode produces electrons oxygen electrode accepts electrons
Explain why a fuel cell does not need to be recharged
hydrogen (fuel) is continuously supplied/fed in
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
greater proportion of energy is available from hydrogen-oxygen reaction, less energy wasted as thermal energy
Identify one major hazard associated with the use of a hydrogen–oxygen fuel cell in a vehicle
hydrogen is flammable/explosive
where does the most negative electrode go
the left has most negative electrode potential
how do you calculate cell emf
right - left
Fe3+ + e- → Fe2+ - 0.77 V Cu2+ + 2e- → Cu + 0.34 V Identify the negative electrode in the half equation above
Fe3+ + e- → Fe2+