Electrochemistry Flashcards
Batteries
How do rechargeable batteries work?
By connecting the cell to an external circuit. This will provide electrical energy to force the electrons in the other direction, and drive the reaction backwards.
Explain discharging:
When a battery is being used as normal to power something, the reaction which occurs is the spontaneous reaction (normal).
More positive half equation goes forward, more negative goes backwards.
Explain recharging:
When a battery is connected to an external voltage, the reaction which occurs is the reverse of the normal spontaneous reaction.
What must be true about the cell reaction for the cell to be able to be recharged?
The reaction must be reversible.
The products of the reaction must stay near the electrodes.
If, for example, the product is a gas, then it will escape and can’t be tuned back into reactants.
What are some advantages of rechargeable batteries, over non-rechargeable ones?
- Can reuse them, so les environmental damage extracting the metals
- Less waste, many metals used in batteries are harmful to the environment (cadmium and lead in particular).
What are some disadvantages to rechargeable batteries over non-rechargeable ones?
Fossil fuels may be used to provide the voltage for recharging, leading to the release of greenhouse gases.
What’s the definition of a fuel cell?
Electrochemical cells where the reactants are continuously supplied.
What are 2 advantages of using a hydrogen-oxygen fuel cell.
- Only waste material is water, so no carbon dioxide emissions. (This is an advantage over combustion engine).
- Since fuel cell is constantly supplied, you don’t need to recharge the cell (as long as you have a continuous supply of fuel available). This is an advantage over using a battery.
What are 3 disadvantages of using a hydrogen-oxygen fuel cell?
- Producing the hydrogen may use energy from fossil fuels, which leads to greenhouse gas emissions.
- Hydrogen is explosive (safety issue)
- Storage - hydrogen is the lowest density gas there is, so it takes up a lot more volume than petrol with the same energy content.
What is the standard electrode potential of the H+/H2 electrode?
By definition, must be zero.
The EMF of the acid hydrogen -oxygen fuel cell is the same as the alkaline hydrogen-oxygen fuel cell.
Explain this result.
Same overall reaction.
A Daniel cell was set up using 100cm3 of a 1.0moldm3 copper sulphate solution.
The cell was allowed to produce electricity until the concentration of copper ions had decreased to 0.5moldm3.
Briefly outline how you would carry out this experiment to confirm the mass of zinc electrode decreasing:
Allow cell to discharge until concentration of copper ions is 0.5.
Confirmed by colorimetric measurement.
Weigh the Zn electrode before and after the experiment.
State one essential requirement of the soluble ionic compound it make the salt bridge:
Must not react with the ions in the solution.
