Energy Changes Flashcards
How does a H-O fuel cell produce electricity
Hydrogen enters the cell and is oxidised at the anode (negative)
This sets up a potential difference across the cell
So the electrons flow from the anode to the cathode through an external circuit
producing an electric current which can power something
Half equation for the cathode in a fuel cell
H2 -> 2H(+) + 2e(-)
Half equation for anode in fuel cell
O2 + 4H(+) + 4e(-) -> 2H2O
Because you need 2 Hydrogen atoms to react with one oxygen atom
Advantages of fuel cells (vs rechargeable batt)
Only waste product is water (and heat) so they don’t leave toxic waste at disposal
Faster to refuel (than recharging batteries)
Hydrogen CAN BE renewable if renewable energy is used for electrolysis
Continue to work as long as hydrogen is supplied (no recharge needed)
Store more energy than rechargeable (further distances…)
Disadvantages of fuel cells
They produce less potential difference than rechargeable batteries
Hydrogen is an flammable gas which is difficult to store safely
Rechargeable batteries dont need fuel continually supplied
Takes up lots of space to store
Hydrogen is often made from hydrocarbons or electrolysis (which uses electricity… fossil fuels…)
Overall equation for hydrogen fuel cell
2H2 + O2 –> 2H2O
How does a battery work? (Contact, potential difference, charge)
Two metals of different reactivities connected by a wire in contact with an electrolyte which contains ions that react with them.
The chemical reactions set up a potential difference between the electrodes
So the charge can flow through the wire and electricity is produced.
What effect does a greater difference in electrode reactivity have? What else can affect this?
Greater potential difference produced (results in more power)
Type of electrolyte
Why is there a difference in charge when two different metals are in the same electrolyte.
Both electrodes react differently with the electrolyte
Why do non rechargeable batteries have a limited lifespan?
Over time the ions in the electrolyte and the electrodes are used up and formed into reactants.
Once any one is used up the reaction can no longer happen. Reaction cannot be reversed.
How do rechargeable batteries work and why is their lifespan also limited
Reaction is reversed when an external current is applied
They can only be recharged so many times
How can you determine the orders of reactivity given a graph of the voltage produced in a battery?
The higher the potential difference, the greater the reactivity.
If it is negative, the left electrode is more reactive
A newspaper article referred to the hydrogen fuel cell powered trains as the new steam trains
Suggest why
Hydrogen is oxidised to produce water in fuel cells
Water is produced as vapour in steam trains
Balancing half equations mistake
Make sure to balance the electrons as well
If the first electrode is less reactive than the second is the voltage positive or negative
Positive
