Rechargeable vs Non rechargeable vs Fuel cells Flashcards
when do the chemical reactions stop in a non rechargeable cells
when one of the reactants have been used up
what is an example of a non rechargeable battery
alkaline batteries
why can rechargeable cells be recharged
when in use the chemical reaction goes forward to release electrons etc
however
when attached to external electrical current the backward reaction occurs and re makes the chemicals
what is the difference with a fuel cell composition
uses an external source of fuel like hydrogen and oxygen or air
what happens to the fuel in the cell
it is electrochemically oxidised to produce a potential difference
what is the reaction in a hydrogen fuel cell
oxidation of hydrogen to produce water
what is the formula and half equations for what happens in a hydrogen fuel cell
2H2(g) + O2 (g) – >2H2O (l)
Negative electrode
2H2 + 4OH- —> 4H2O + 4e-
Positive electrode:
O2 + 2H2O + 4e- —> 4OH-
what happens in a hydrogen fuel cell
hydrogen enters the cell and is oxidised which creates a potential difference across the cell
what are the pros of hydrogen fuel cells
they do not degrade or need replacing
their waste product of water is not bad for environment
only need hydrogen and oxygen
what are the cons of hydrogen fuel cells
gas which increases storage amount
H2 is flammable
requires energy to make Hydrogen in first place from fossil fuels
What is the equation for overall reaction which takes place in hydrogen fuel cell
2H2 + O2 —> 2H2O
What does a hydrogen fuel cell look lik
On the left H2 Enters and is met with a negative electrode
On the right O2 enters and is met with a positive electrode
inbetween the electrodes is an electrolyte and a wire connecting both the electrodes
What does hydrogen do once it enters
difuses across negative electrode and reacts with OH- ions to form water
