Electrochemisry Flashcards
(27 cards)
In a Zinc half cell, what are the two possible reactions?
- Zn could be oxidised and move into the solution.
- Zn2+ could be reduced ad move out of the solution.
What is the purpose of the salt bridge in an electrochemical cell?
Allows ions to flow to complete the circuit.
What is the salt Brigid made up of in an electrochemical cell?
Filter paper soaked in a KNO3 cell.
How do you remember what side of the electrochemical cell is negative/positive, oxidation/reduction?
Left
Oxidation
Negative
Recall th conventional way of drawing cell diagrams. Give an example for Zn and Cu?
Zn|Zn2+||Cu2+|Cu
In a half cell, if there i no metal, what is the electrode made of?
Pt, platinum
Define standard electrode potential?
The potential to a redox system to lose or gain electrons compared to thee standard hydrogen electrode.
Recall the standard conditions?
- All solutions ave concentration of 1.00 moldm-3
- All gases have pressure 100kPa
- Temperature 298K
- Pt electrode if no metal
Recall the S.H.E
- H2 gas bubbled into a solution of 1M H+ ions.
- 2H+ +2e- <—> H2
- Pt electrode converted in finely divided Pt for a large surface area.
- Electrode potential is 0
- Always on the left
What is the requirement of the salt bridge?
Most not react with the electrolyte.
How are reactions written in the electrochemical series?
As reductions
An oxidising agent will oxidise anything that is ____ it in the electrochemical series.
Above
A reducing agent will reduce anything ______ it in the series.
Below
What are the equations to predict whether a redox reaction will happen?
E = E reduction - E oxidation (for a reaction)
E = E right - E left ( for a cell )
E must be over 0 for the reaction to occur
What are the two reasons an expected reaction would not happen in a cell?
- Kinetically stable (Ea too high)
- Solutions too dilute ( not standard conditions )
A change which favours reduction
E = more +ve
A change which favours oxidation
E = more -ve
What are the two reactions that occur in a lithium cell?
Positive electrode: li+ + CoO2 + e- —> Li+[CoO2]-
Negative electrode: Li —> Li + e-
What are the advantages for non-chargeable batteries?
- Cheaper to buy.
- Work for longer.
- Can be recycled.
- Don’t contain toxic metals e.g. Pb meaning it’s less dangerous in a landfill.
What are the advantages of rechargeable batteries?
- Can be reused so cheaper one term.
- Can be recycled.
- Less need to be produced.
What are the advantages of fuel cells?
- No recharging needed.
- Water as the only product.
What are the disadvantages of fuel cells?
- Expensive as H2 produced by electrolysis of water.
- H2 is highly flammable.
Recall the conventional cell diagram for a H-O fuel cell
Pt | H2 | H2O || O2 | OH- | Pt
When and why are Pt electrode used in cells?
- Used when a system doesn’t include a metal that can act as an electrode.
- Pt = unreactive + conducts electricity.
