Electrochemical Cells Flashcards
What is a half cell?
One half of an electrochemical cell which can be constructed of a metal dipped in its ions or a platinum electrode with 2 aqueous ions
What is an electrochemical cell made up of?
- 2 half cells
- Wire
- Voltmeter
- Salt Bridge
Why is the process described as a redox reaction?
process and the other is undergoing an oxidation process
In the diagram, what is being oxidised, state the observation and the equation?
Zinc half cell shows loss of electrons as zinc loses electrons easier than copper (Oxidation)
Zn ↔ Zn2+ + 2e-
Observation – Zinc electrode will become thinner as more Zn2+ is produced to make electrons
In the diagram, what is being reduced, state the observation and the equation?
Copper half cell accepts the electrons produced by zinc (Reduction)
Cu2+ + 2e- ↔ Cu
Observation – Copper electrode will get thicker as Cu2+ ions receive the electrons and turn into copper.
What form are equations written it?
Reduction form
What does Electrode potential (Eꝋ) shows and what are the units?
How easily the half cell gives up electrons (oxidised) and is measured in Volts
Why is a Standard Hydrogen Electrode (SHE) used?
Because Electrode potentials can’t be measured on their own but we can measure against a reference cell called a SHE as the Eꝋ = 0.00V and also used for reaction feasibilty
What are the standard conditions?
- Temperature = 298K
- Pressure = 100kPa
- Concentrations of ions = 1 mol dm-3
Explain the Electrochemical Series
- Agents on the left hand side of the equation are more easily reduced as they have an increasing tendency to gain electrons
- Agents on the right hand side of the equation are more easily oxidised as they have an increased tendency to lose electrons
What is the formula to calculate the Standard Cell Potential (Eꝋcell)?
Eꝋcell = Eꝋreduced - Eꝋoxidised
What is cell notation?
It is the standard way of representing cells in chemistry
What is the standard cell notation representation?
Reduced Form | Oxidised Form || Oxidised Form | Reduced Form
What decides what goes on the left and right hand side of the double line?
The most negative half cell potential goes to the left of the double line
What does the single line represent?
Shows a physical state change
What does the double line represent?
It shows a Salt Bridge
When do we use a platinum electrode?
When using 2 non metals
How can you tell if a reaction is feasible?
A reaction is feasible if the Eꝋcell value is positive using the equation
What are Batteries?
They are electrochemical cells that come in 2 forms:
• Rechargeable
• Non-rechargeable
What is an electrolytes function?
It acts as a conductive pathway for ions to move from one electrode to another
Explain the comparison when deciding to use non – rechargeable and rechargeable?
Non – rechargeable batteries tend to be cheaper than rechargeable batteries, however, rechargeable batteries are reversible and last longer which means they are cheaper in the long term
What is an example of rechargeable batteries?
Lithium ion batteries
What is an example of non – rechargeable batteries?
Zinc carbon batteries
Explain how the Zinc Carbon electrochemical cell is setup?
It has a Zinc positive electrode and a mixture of manganese dioxide + carbon for a negative electrode.
Which electrolyte is sued for zinc carbon batteries?
Ammonium Chloride
What are the 2 half equations for Zinc Carbon batteries?
- Zn –> Zn2+ + 2e-
* 2MnO2 + 2NH4+ + 2e- –> Mn2O3 + 2NH3 + H2O
Explain how the Lithium electrochemical cell is setup
A lithium cell (one type) is made from Lithium cobalt oxide (LiCoO2) electrode and a graphite electrode
Which electrolyte is used for lithium cells?
Lithium Salt
What are the 2 half equations for lithium cells?
- Li + CoO2 + e- ↔ Li[CoO2]-
* Li ↔ Li+ + e-
How do you recharge batteries?
Current supplied forcing electrons in opposite direction around circuit and reverse reaction and this is possible as none of the substances escape or used up
Explain how a fuel cell works (Alkaline hydrogen – oxygen fuel cell)
1) Hydrogen is fed in here. It reacts with OH- ions in solution in (9) but reaction is:
H2 + 2OH- 2H2O + 2e-
2) Electrons produced in step 1 travel through Platinum electrode
3) This is the flow of electrons to power circuit
4) Oxygen is fed in here. It reacts with water and 4 electrons from step 1 to make OH- ions: O2 + 2H2O + 4e- 4OH-
5) Electrons flow to negative electrode which is made from platinum
6) Electrolyte made from KOH solution. It carries OH- from cathode to anode
7) Electrons flow from positive electrode which is made from platinum
8) Product from step 1 (H2O) is released to surroundings
9) OH- ions produced from step 4 carried towards anode via electrolyte
State 3 advantages of Fuel cells
- Fuel cells are more efficient as more energy is converted to kinetic energy
- Doesn’t need to be recharged; just use supply of H2 + O2
- Only waste product is water
State 3 disadvantages of Fuel cells
- Hydrogen is highly flammable so must be stored correctly
- Expensive to transport and store H2 as it’s in pressurised containers
- Energy is required to make H2 + O2. Fossil fuels used to pass water through electrolysis which contributes to CO2 emissions
