Redox and galvanic cells Flashcards
Oxidation and reduction
Interdependent, simultaneous, electron transfer process
Oxidation
Involves losing electrons (Lose Electron Oxidation, LEO)
Reduction
Involves gaining electrons (Gain Electron Reduction, GER)
Oxidising agent
Substance that has the ability to remove electrons from a substrate, substance that is reduced
Reducing agent
Substance that has the ability to donate electrons to a substrate, substance that is oxidised
Anode
Involves oxidation, loses mass
Cathode
Involves reduction, gains mass
Galvanic cells
Redox reactions generate electricity if the two half-reactions are physically separated so that the transferred electrons can be directed through an external circuit (produces power)
Purpose of galvanic cells and electrolytic cell
Galvanic- Turn chemical potential energy into electrical energy
Electrolytic- Turn electrical energy into chemical potential energy
What does the salt bridge do in a galvanic cell
Maintains electrical neutrality, Completes circuit, Facilitates ion movement
Why may the voltage reading not be accurate to calculations
Not being at standard conditions, Not accurate/correct concentration of solutions
Primary batteries- dry cell
Single use, Oxidation: Zn —> Zn2+ + 2e, Reduction: 2MnO2 + 2NH4+ + 2e- —> Mn2O3 + H20 + 2NH3, Porous separator between cathode and anode which acts as a site for electron transfer, Moist paste which allows flow of charge (cations and anions), Moist past contains NH4Cl which provides needed acidic conditions, Anode is the negative terminal
Secondary batteries- lead accumulator
Rechargeable, Cathode: PbO2 + 4H+ + SO4 2- <—> 2H2O + PbSO4, Anode: Pb + SO4 2- <—> PbSO4 + 2e-, Discharge: Pb + 2SO4- + 4H+ + Pbo2 —> 2PbSO4 + 2H2O, causes decrease in pH, H2SO4 acts as the electrolyte, forms a precipitate
Fuel cells
Anode: 2H2 + 2OH- —> 2H20 + 2e-, Cathode: O2 + 2H2O + 4e- —> 4OH-, Continuous supply of oxygen and hydrogen (from fossil fuels), Porous electrode of nickel or platinum which acts as a catalyst, High temperature makes it less efficient, Acidic or alkaline conditions, Constant rate or electricity- depends on reaction rates
Half reactions in galvanic cells vs electrolytic cells
Galvanic- spontaneous (positive E value), separate half-reactions
Electrolytic- Non-spontaneous (negative E value), Half reactions not separate (all in one container) but sometimes products need to be separated