C20- Electrochemical Cells Flashcards
What is a half cell?
This is a half cell and the strip of metal is an electrode. The position of the equilibrium determines the potential difference between the metal strip and the solution of metal.
What is an electrochemical cell?
Most electrochemical cells consist oftwo solutions with metal electrodesand asalt bridge. A salt bridge is a tube ofunreactive ions(KNO3, KCl and NaNO3) that can move between the solutions to carry the flow of charge but will not interfere with the reaction.
What is the standard hydrogen electrode?
The standard hydrogen electrode is themeasuring standardfor half-cell potentials. It has a cell potential of0.00V, measured understandard conditions. These conditions are:
- Solutions of1.0 moldm3concentration
- A temperature of298K
- 100 kPapressure
Why is the standard hydrogen electrode 0?
To compare other half cells
What are the reactions that take place in a standard hydrogen electrode?
The cell consists ofhydrochloric acid, hydrogen gasand usesplatinum electrodes. These are very useful as they aremetallic, so will conduct electricity, but are alsoinertso will not interfere with the reaction.
Reduction: 2H⁺(aq) + 2e⁻ ⇌ H₂(g)
Oxidation: H₂(g) ⇌ 2H⁺(aq) + 2e⁻
The overall equation is:
2H⁺(aq) + H₂(g) ⇌ H₂(g) + 2H⁺(aq)
What is a cell potential?
If measured understandard conditions, cell potentials are measured compared to theSHEto give a numerical value for the half-cell potential.
Negativepotentials mean the substances are more easilyoxidisedand willlose electrons.Positivepotentials mean the substances are more easilyreducedand willgain electronsto become more stable.
What are the strongest oxidising and reducing agents?
Strong the oxidising agent more likely to reduce and vice versa.
What are the effects of concentration and pressure?
Increasing the concentrationof the solutions used in the electrochemical cell makes the cell EMF morepositiveas fewer electrons are produced in the reaction.
Increasing the pressureof the cell will make the cell EMF morenegativeas more electrons are produced.
How can you tell if a reaction is feasible or not?
Predicting the direction of redox reactions: the electrode with a more negative electrode potentials have a lower tendency to accept electrons. When a pair of electrodes are connected, electrons flow from the more negative to the more positive. The signs of the electrodes can be used to predict direction of the reaction.
How does a lithium ion cell work?
Lithium ion cells are rechargeable batteries used in portable electronics and electric vehicles. They use a lithium cobalt oxide cathode, a graphite anode, and a lithium salt electrolyte to store and transfer electrical energy.
Li+ Li+ + CoO2 -> Li+ + Li+[CoO2]-
How do rechargeable batteries work?
In order to be recharged, acurrent has to be appliedover the cell which forces electrons to move in theopposite direction. This causes the reaction to reverse, recharging the cell.
What are fuel cells?
This type of electrochemical cell is used to generate an electrical current without needing to be recharged. The most common type of fuel cell is thehydrogen fuel cell, which uses acontinuous supplyof hydrogen and oxygen from air to generate acontinuous current.
What are the reactions in a hydrogen fuel cell?
H20
