Electrode Potentials Flashcards
Where is equilibrium if there is a large voltage
To the right
Where is equilibrium if there is a small voltage
To the left
What does the voltmeter do
Prevents electrons flowing
What does the salt bridge do
Completes the circuit and allows flow of ions
Why is platinum a suitable electrode
Unreactive and conducts electricity
Standard hydrogen electrode
Used to compare single electrodes and voltage is 0
H2 gas pumped in at 100kpa
Solution of h+ conc is 1moldm-3
Must be a platinum electrode
Temp must be 298k
What is the voltage of standard hydrogen electrodes
0v
Electrode potential value oxidation
Most negative value more likely to show oxidation
Electrode potential value reduction
Most positive value more likely to show reduction
Conventional cell representation.
Zn|zn2+||cu2+|cu|pt
One line = phase boundary if same state use comma
Two lines = salt bridge
At other on end if platinum electrode
Reduction on right and oxidation on left
EMF
EMF = reduction - oxidation
What happens if condition are changes
Equilibrium will shift
Condition changing examples for mg2+
Decrease
Equilibrium opposes the decrease in concentration of mg2+ and shifts to the left hand side
So electrode potential value becomes more negative as there is an increase in electrons
So emf becomes more positive
Single use battery
Reaction is irreversible
Rechargeable batteries li(coO2)
Negative electrode
Li->li+ +e-
Positive electrode
CoO2 + li+ + e- -> Li(CoO2)
Overall equation
CoO2 + li -> Li(CoO2)
Equation when recharging
Flip everything
Fuel cell
Uses the energy from the reaction of a fuel with oxygen to create a voltage.
Advantages of fuel cell over fossil fuels
Greater efficiency than burning h2 in a combustion engine
Less polluting as water is only product
Disadvantages of using fuel cell over fossil fuels
H2 is difficult to store
Fossil fuels are combusted to produce the hydrogen which release co2
Advantages of fuel cells to other types of cell
Voltage is constant as fuel and oxygen is supplied constantly so concentrations of reactions remain constant
Hydrogen oxygen fuel cell in alkaline solution
At anode
H2 + 2oh- <-> 2h2o + 2e- Oxidation. -0.83
At cathode
1/2o2 + h2o + 2e- <-> 2oh- Reduction. +0-40
Overall equation
H2 + 1/2o2 -> h2o. 1.23
Hydrogen oxygen fuel cell in acidic solution
Anode
H2 <-> 2h+ + 2e- 0.0
At cathode
1/2 o2 + 2h+ +2e- <-> h2o 1.23
Overall equation
H2 + 1/2o2 -> h20. 1.23
Ratio of cr2o72- to fe2+
1:6
