Electrode potentials and cells Flashcards
In an electrochemical cell, what is the purpose of the salt bridge?
It allows ions to flow through to balance out the charges
Which salt solution is the salt bridge soaked in?
Potassium nitrate
Why is a high resistance voltmeter used?
It stops the current flowing in the current which makes it possible to measure the maximum possible potential difference.
Why is a wire not used?
The metal wire would set up its own electrode system with the solutions.
What happens to the voltage when the current is allowed to flow?
The voltage will fall to zero as the reactants are used up
If a system does not include a metal that can act as an electrode, which electrode is used and why?
Platinum
- it is inert
- it conducts electricity
What is the standard electrode potential of a half cell?
It is the voltage measured under standard conditions when the half cell is connected to a standard hydrogen electrode
What are the standard conditions?
pressure- 100kPa
concentration - 1 mol/dm3
temperature - 298K
Why are standard conditions needed when measuring the standard electrode potential?
the position of the redox equilibrium will change with conditions
What is the formula used to calculate the standard cell potential when two half cells are joined together?
E(cell) = E(reduced) - E(oxidised)
How can electrode potentials be used to predict the feasibility of a reaction?
If the E(cell) value is positive, then the reaction is feasible
Give the electrode reactions in a lithium cell
Positive electrode:
Li+ + CoO2 + e- → Li[CoO2]-
Negative electrode:
Li → Li+ + e-
How is a rechargeable battery recharged?
A current is supplied to force the electrons to flow in the opposite direction around the circuit and reverse the reactions.
Give the electrode reactions in a hydrogen fuel cell in alkaline conditions
Positive electrode:
O2 + 2H2O + 4e- → 4OH-
Negative electrode
2H2 + 4OH- → 4H2O + 4e-
Why do fuel cells maintain a constant voltage over time?
They are continuously fed with fresh oxygen and hydrogen so maintaining a constant concentration of reactants
