State the difference between galvanic cell and electrolytic cell.
Galvanic cell: Conversion of chemical energy to electrical energy, the redox reaction is spontaneous
Electrolytic cell: Conversion of electrical energy to chemical energy, redox reaction is non-spontaneous
Water is not considered in galvanic cell as its Electrode potential is too positive and hence the forward reaction is always favoured
What are galvanic cells?
Galvanic cells are electrochemical cells in which redox reactions occur spontaneously to generate chemical energy.
What takes place at the anode and cathode in a galvanic cell?
Oxidation occurs at the anode and the anode is the negative electrode as electrons are produced at the anode during oxidation.
Reduction occurs at the cathode and the cathode is the positive electrode as it receives the electrons for the reduction reaction.
What is the function of the salt bridge?
- Prevent direct mixing of the two different solutions but allowing the passage of ions between the two half-cells to complete the electrical circuit.
- Helps to maintain electrical neutrality in each half cell.
What does the value of the electrode potential show?
A positive electrode potential shows that equilibrium position lies more to the right, hence reduction process is favoured.
A negative electrode potential shows that equilibrium position lies more to the left, hence oxidation process is favoured.
State the factors affecting electrode potential.
- Nature of metal: If a metal is highly electropositive, the metal atoms have a greater tendency to lose electrons and become positive ions, hence POE lies more to the left and electrode potential is negative.
- Concentration of metal ions: If concentration of the hydrated metal ions is decreased, the POE shifts left o replenish the metal ions removed, hence electrode potential is more negative
- Temperature: If temperature increases there is an increasing tendency for the metal to dissolve in the solution and form hydrated metal ions, POE shifts left and electrode potential becomes more negative
- Pressure of gaseous species: when pressure increases, POE shifts right to reduce the number of gaseous molecules and electrode potential becomes more positive.
State the standard conditions for electrode potentials.
1 bar, concentration of aqueous ions of 1moldm^-3
Define standard electrode potential.
Standard electrode potential of an electode is the relative potential of this electrode under standard conditions compared with the standard hydrogen electode whose electrode potential is assigned as 0V.
What does the standard hydrogen electrode consist of?
It consists of H2(g) at 1 bar bubbling over platinum electrde coated with finely divided platinum which is dipped into 1 moldm^-3 H+(aq).
If standard conditions are not acieved the hydrogen electrode potential is not zero.
How does the electrode potential reflect the oxidising/reducing power of the species?
The more positive electrode potential, the greater tendency for the species on the LHS to be reduced, stronger oxidising agent.
The more negative e;ectrode potential, the greater tendency for the species on the RHS to be oxidised, stronger reducing agent.
Define standard cell potential.
Standard cell potential is the emf of a galvanic cell which consists of two half-cells connected under standard conditions. The Ecell value is the difference between the two standard electrode potentials.
Ecell = Ereduction - Eoxidation
How do we predict whether a redox reaction occurs using Ecell?
If Ecell > 0V, the forward reaction is energetically feasible, hence it is spontaneous under standard conditions.
If Ecell < 0V, the forward reaction if not energetically feasible, however the reverse reaction is expected to be spontaneous under standard conditions.
If Ecell = 0V, an equilibrium is established.
State the equation relating Gibbs free energy and Ecell.
Change in G = -nFEcell where n is the number of electrons per mole reaction and F is the Faraday’s constant (9.65 x 10^4 Cmol-1)
spontaenous reaction (G<1) hence Ecell>0
What is electrolysis?
Electrolysis is a process in which electrical energy is used to induce non-spontaneous redox reactions.
State the reactions occuring at the anode and cathode in a electrolytic cell.
Anions are oxidised at the anode as they lose electrons, however it is the positive electrode as it attracts anions.
Cations are reduced because they gain electrons, however it is the negative electrode as it attracts cations.
State the formula to find the quantity of charge.
Q = I x t
I: current in amperes t: time in seconds
State the formula linking the Faraday’s constant and the charge of 1mole of electrons.
F = Le
F: Faraday’s constant 96500
L: Avogadro’s constant 6.02 x 10^23
e: charge of one electron 1.60 x 10^-19
State the formula linking the amount of electrons that passed through a circuit and the total charge passed through.
Q = n x F
Q: charge
n: no. of moles of electrons
F: Faraday’s constant 96500
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Atomic Structure22
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Chemical Bonding32
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Gaseous State9
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Periodicity26
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Mole Concept and Stoichiometry5
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Energetics38
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Reaction Kinetics36
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Chemical Equilibria28
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Acid Base Equilibria33
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Solubility Equilibria11
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Intro to Organic Chemistry25
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Alkanes18
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Alkenes21
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Arenes15
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Halogen Derivatives28
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Hydroxy Compounds29
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Carbonyl Compounds23
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Carboxylic Acids and Derivatives24
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NItrogen Compounds31
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Electrochemistry18
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Introduction to Transition Elements32
