Applications: Electrochemical cells
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In a cell’s negative electrode, what electrode is present and what occurs?
Smaller EMF electrode e- lost via oxidation
In a cell’s positive electrode, what electrode is present and what occurs?
Higher EMF electrode e- gained via reduction
What does the potential difference do within an electrochemical cell
Drives an electric current to do work
In electrochemical cells, what is between each electrode
A salt bridge
Function of electrochemical cells
Commercial source of eletrical energy
Conditions effecting EMF
Non standard conditions EMF decreases with use - chemical reactants used up
3 different types of cells
Non-rechargeable Rechargeable Fuel cells
Advantage and disadvantage of non-rechargeable cells
Good: Cheaper to buy Bad: Single use, finite, toxic substances
Advantage and disadvantage of rechargeable cells
Good: Minimise waste, less resources needed Bad: More expensive
Why are some cells rechargeable?
As the reactions can be reversed
Positive and negative electrode reactions in a lithium ion cell
Positive electrode: Li+ + CoO2 + e– → Li+[CoO2]– = 0.9V Negative electrode: Li → Li+ + e– = -3.04V
Why is water not used as an electrolyte for lithium ion cells
Lithium would react with the water to produce LiOH
Overall reaction and EMF of a lithium ion cell
Li + CoO2 -> Li+[CoO2]- 2.91V
What way do e- travel in a circuit
From negative to positibe (left to right)
Write a half equation for the reaction that occurs at the positive terminal of the cell Li(s) | Li+(aq) || Li+(aq) | MnO2(s), LiMnO2(s) | Pt(s)
Use the positive (RHS) of the cell representation Li+ + MnO2 + e- -> LiMnO2
What do fuel cells generate?
An eletric current
Properties of fuel cells
Do not need to be electrically recharged Concentrations remain constant EMF does not change with use
Why are fuel cells highly efficient
Less proportion of energy is converted into heat energy
Positive and negative electrode reactions in an alkaline hydrogen-oxygen fuel cell (acidic conditions)
Positive: O2 + 4H+ + 4e- -> 2H2O Negative: H2 -> 2H+ + 2e-
Positive and negative electrode reactions in an alkaline hydrogen-oxygen fuel cell (alkaline conditions)
Positive: O2 + 2H2O + 4e- -> 4OH- Negative: 2OH- + H2 -> 2H2O + 2e-
Overall reaction and EMF of hydrogen-oxygen fuel cells
2H2(g) + O2(g) -> 2H2O(l) 1.23V
Advantages & Disadvantages of hydrogen-oxygen fuel cells
Good: Water is the only product so no CO2 or SO2 released. Efficient. Bad: Fossil fuels burned to generate hydrogen.