3.1.11 Electrode potentials and electrochemical cells Flashcards
How do you write cell notation?
R|O||O|R
What is the function of a salt bridge?
Allows ions to move across the salt bridge and completes the circuit
Give the characteristics of solution used in the salt bridge, what are some common examples?
- Inert, should not react with either electrolyte
- Any reaction that did occur would change the cell EMF
- KCl, AgNO3 and NaCl
When preparing a metal electrode like aluminium, why should you clean the piece of metal using sandpaper?
Removes the oxide layer (impurity)
When is the Pt (s) electrode required?
When there is no solid metal electrode present
At what electrode does reduction occur.
- RHS
- Cathode (+ve)
At what electrode does oxidation occur.
- LHS
- Anode (-ve)
What are the standard conditions in an electrochemical cell?
- 1 moldm-3
- 298 K
- 100 kPa
What is the SHE and what is its role in calculating standard elctrode potentials?
Standard hydrogen electrode
- All other electrodes are compared to this standard value (0.00V)
- Measured relative to SHE
How do you calculate the standard electrode potential of a cell?
EΦcell = EΦ(RHS) - EΦ(LHS)
When is a reaction feasible and not deasible in terms of the EΦcell value?
When EΦcell < 0 : not feasible
When EΦcell > 0 : feasible
When a half-cell has a more positive EΦcell is it oxidised or reduced in the reaction?
Reduced
- This is the positive cathode
- Electrons flow from negative to positive cathode
Give examples of:
a) rechargeable cell
b) non-rechargeable cell
c) fuel
a) Lead-acid batteries, lithium cells
b) Zinc-carbon cells
c) Hydrogen-oxygen fuel cells
Give an equation for the reaction that occurs at the positive lithium cobalt oxide electrode.
Li+ + CoO2 + e– → LiCoO2-
Why can you not recharge a zinc-carbon cell (or any non-rechargeable cell)?
The reaction is impossible to reverse
How do you recharge a cell and why do you not need to recharge a fuel cell?
- Current is applied which forces the elcetrons in the opposite direction
- Reactents of a fuel cell are supplied continuosly
Suggest one reason why many waste disposal centres contain a separate section
for cells and batteries.
- Prevents pollution of the environment y toxic compounds found in the cells
- Compounds can leach into environment when placed in landfills
How may the recharging of a cell lead to the release of CO2 into the atmosphere?
Requires energy which may have come from the burning of fossil fuels in power stations
Why might a rechargeable cell be connected to a solar cell sed to power road signs?
- Solar cell does not work all the time, only when it is light out
- Rechargeable cell can store electrical energy and work when the solar cell is not
What are the half cell reactions in a hydrogen-oxygen fuel cell?
H2 + 2OH- → 2H2O + 2e-
O2 + 2H20 + 4e- → 4OH-
Suggest the main advantage of using hydrogen in a fuel cell rather than in an internal combustion engine of a car.
In the fuel cell, a greater proportion of energy available from the hydrogen-oxygen reaction is converted into useful energy
Highlight the postives and negatives of non-rechargeable cells?
Positives:
Negatives: can’t recharge, lots of waste
Highlight the postives and negatives of rechargeable cells?
Positives: recharge, less waste
Negatives: requires energy to recharge that can come from fossil fuels (carbon dioxide)
Highlight the postives and negatives of fuel cells?
Positives: only water produced, less damage to environemnt, no harmful nitrogen oxides produced
Negatives: relies on crude oil (non-renewables), hydrogen gas is highly flammable
