electrochem Flashcards
How are electrochemical cells made?
Made from 2 different metals dipped in salt solutions of their own ions and connected by a wire
What type of process is an electrochemical cell?
Redox
How do electrons flow through the wire?
From the most reactive metal to the least
How do we measure the voltage in the cell?
Using a voltmeter in the external circuit (wire). AKA the cell potential or EMF
What does the direction of the reaction at each electrode depend on?
How easily the metal loses its electrons (i.e. how easily its oxidised)
How do we measure how easy it is to oxidise a metal?
Using electrode potentials. Metals that are easily oxidised have very negative electrode potentials, whereas ones that are difficult to oxidise are more positive
How do we write electrochemical cells, using zinc and copper as an example?
Zn (s) | Zn 2+ (aq) || Cu 2+ (aq) | Cu (s)
Which half cell goes on the left?
The one with the more negative electrode potential on the left.
How do you calculate cell potential?
Eºcell = Eºright - Eºleft
OR
Eºcell = Eºreduced - Eºoxidised
Is the cell potential negative or positive?
The cell potential will always be positive, because youre taking away the more negative value from the more positive value
What are standard conditions?
Concentration of 1.00 moldm-3 for solutions of ions
Temperature of 298K (25ºC)
Pressure of 100kPa
What is the standard hydrogen electrode?
Hydrogen gas is bubbled through a solution of aqueous H+ ions. A platinum electrode is used as the platform for oxidation/reduction
What is the standard electrode potential of a cell?
The voltage measured under standard conditions when the half cell is connected to the standard hydrogen electrode
Where is the standard hydrogen electrode written in a representation of the cell?
Always on the left. Does not matter if the other half cell has a more positive value
What is the electrode potential of the standard hydrogen electrode?
0.00V
What is the electrochemical serie?
A list of electrode potentials for different electrochemical half cells in order to
In what order is the electrochemical series written?
The most negative at the top, going down to the most positive
Most negative= best reducing agent
Most positive= best oxidising agent
What are different commercial types of electrochemical cells?
Non-rechargeable, rechargeable and fuel cells
What are non-rechargeable cells?
In these cells, the chemicals are used up over time and the emf drops. Once one or more of the chemicals is entirely used up, the cell is flat and the emf is 0V. These cells cannot be recharged and have to be disposed of after their single use
What are rechargeable cells?
In these cells, the reactions are reversible, and these are reversed by applying an external current to regenerate the chemicals
What are two examples of non rechargeable cells?
Zinc-carbon- cheap but fairly short life
Alkaline (zinc and MnO2) more expensive but longer life
What are three examples of rechargeable cells?
Lithium ion- used in phones or tablets etc
Lead acid- made of six cells and used in cars
Nickel-cadmium - standard rechargeable batteries
What are fuel cells?
They have a continuous supply of the chemicals into the cell and so neither run out of chemicals or need recharging. Most common is hydrogen-oxygen fuel cell
What are the half equations for a hydrogen oxygen fuel cell in alkaline conditions?
Anode: 2H2 + 4OH- –> 4H2O + 4e-
Cathode: O2 + 2H2O + 4e- –> 4OH-
What are the half equations for a hydrogen oxygen fuel cell in acidic conditions?
Anode: 2H2 –> 4H+ –> 4e-
Cathode: O2 + 4H+ + 4e- –> 2H2O
What are the benefits of hydrogen fuel cells?
Only waste product is water, don’t need rechargong, very efficient
What are the risks of hydrogen fuel cells?
Need constant supply of fuel, hydrogen is flammable and explosive, hydrogen usually made using fossil fuels, high cost
