5. Energy changes (cells and batteries, fuel cells) Flashcards
What chemicals do cells contain?
Chemicals which react to produce electricity
What is the voltage produced by a cell dependent on?
the type of electrode and electrolyte
How can a simple cell be made?
by connecting two different metals in contact with an electrolyte
What do batteries consist of?
two or more cells connected together in series to provide a greater voltage
What happens in non-rechargeable cells and batteries?
Chemical reactions stop when one of the reactants has been used up
Give an example of a battery that is non-rechargeable?
Alkaline batteries
What happens in rechargeable batteries?
Can be recharged because the chemical reactions are reversed when an external electrical current is supplied
What are fuel cells supplied by?
An external source of fuel. Eg. Hydrogen, oxygen or air
How is the fuel oxidised and what does it produce?
It is oxidised electrochemically within the fuel cell to produce a potential difference
What does the overall reaction in a hydrogen fuel cell involve?
The oxidation of hydrogen to produce water
What do hydrogen fuel cells offer as a potential alternative to?
Rechargeable cells and batteries
Evaluate the use of hydrogen fuel cells in comparison with rechargeable cells and batteries
Hydrogen fuel cells:
- fuel cells can be used constantly provided
fuel keeps being put in
- hydrogen is a gas so needs to be stored at
high pressure and so is harder to
transport
- only produces water when burnt
Rechargeable cells and batteries:
- Can be recharged by reversing reaction, so fuel doesn’t need to keep being supplied
- hard to dispose of - non-biodegradable
- will eventually stop working
What is the half-equation for the cathode in hydrogen fuel cells?
H2(g) –> 2e–+2H+(aq)
What is the half-equation for the anode in hydrogen fuel cells?
4H+(aq) + O2(g) + 4e–→ 2H2O(g)
