Electrode potentials and cell Flashcards
Define the standard electrode potential:
The standard electrode potential of a half cell E° is the voltage measured under standard conditions when the half cll is connected to a standard hydrogen electrode.
If standard conditions maintained the reading on the voltmeter whne a half-cell is connected to the stnadard hydrogen electorde will be the standard electorde potnetial of that half cell.
What are the standard conditions used to measure electrode potentials?
Any solution must have concentration of 1.00 mold-3.
The temperature must be 298K (25°C).
The pressure must be 100kPa.
Whats the electrochemical series?
It is a list of standard elements electrode potentials for different electrochemical half-cells.
Most negative always goes in reverse direction (oxidation).
Most positive (reduction).
How do you calculate standard cell potentials?
E° = E°reduced - E°oxidized
E° = E°right - E°left
(left is the more negative value).
What is the convention for drawing electrochemical cells?
ROOR
Reduced form/ oxidized form// oxidized form// reduced form
(The half cell with more negative potential goes on the left).
How do you use electrode potentials to predict if a reaction will happen?
Combine half equations and any feasible reaction is when E° is positive.
How are electrochemical cells used as batteries?
Batteries are types of electrochemical cells which provide electricity to appliances we use; some can be rechargeable and other can run out.
Non-rechargeable batteries are cheaper than rechargeable batteries. But rechargeable batteries last longer and work out cheaper in the long run.
Give the simplified electrode reaction in a lithium cell:
Lithium cells are used in mobile phones/ laptops. One type is lithium cobalt oxide (LiCoO2) electrode and graphite electrode. The electrolyte is an organic solvent.
The half equations are:
Li+ + e- ⇌ Li (E°= -3.04V)
Li+ + CoC2 + e- ⇌ Li+[CoO2]- (E°= +0.56V)
The Li half cell has more negative E° value so the equation goes backwards:
Li⇌ Li+ + e-
Li+ + CoC2 + e- ⇌ Li+[CoO2]-
To recharge these batteries, a current is supplied to force electrons in the opposite direction around the circuit and reverse the reaction; reactions that take place in non-rechargeable batteries are impossible to reverse).
How can fuel cells generate electricity from hydrogen and oxygen?
In fuel cells chemicals are separately stored. An example is the alkaline hydrogen-oxygen fuel cell which can be used to power electric vehicles. Hydrogen and oxygen gases are fed in two separate platinums containing electrodes. The electrodes are separated by an anion exchange membrane that allows (OH-) and water pass through but it does not hydrogen and oxygen gas. The electrolyte is an aqueous (KOH) solution.
What are advantages of fuel cells?
In comparison to internal combustion engines, fuel cells convert more of their available energy into kinetic energy to get a car moving- internal combustion waste a lot of their energy.
The only waste product is water so theres no nasty toxic chemicals.
They also don’t need to be recharged like batteries as long as hydrogen and oxygens supplied, the cell continues to product electricity.
What are disadvantages of fuel cells?
You need energy to produce a supply of hydrogen and oxygen; this can be done by the electrolysis of water which usually requires electricity (normally generated by burning fossil fuels) which isn’t carbon neutral.
Hydrogen is highly flammable so should be handled carefully when stored/transported.
