Title: Chemistry for Bioscientists I Section C13 Cell Potentials
Course: CHEM10021
University: The University of Manchester
Introduction to cell potentials in relation to bioscientists.
Metal Electrode:
Composed of metal in contact with an ionic solution.
Redox Electrode:
Involves an inert metal in contact with a solution containing a species in two oxidation states.
Gas Electrode:
Consists of a gas in equilibrium with its ionic solution in the presence of an inert metal.
Insoluble Salt Electrode:
Involves a metal (M) coated with an insoluble salt (MX) immersed in a solution containing X- ions.
Vertical Bar (|):
Denotes a barrier (e.g., Ag | AgCl).
Redox Electrode Notation:
Example: "M I Red, Ox" indicates a redox couple Red/Ox.
For instance, NAD+ redox couple as NAD+ + H+ + 2e- → NADH.
Double Vertical Bars (||):
Represent a connection, such as a salt bridge.
Electrolytic Cell Representation:
Example: Pt | NADH, NAD+, H+ || H2O2, H+, O | Pt.
Anode Reaction:
Left-hand half-cell: NAD+ + H+ + 2e- → NADH.
Cathode Reaction:
Right-hand half-cell: O2 + 2H+ + 2e- → 2H2O2.
Overall Cell Reaction:
NADH + O2 + H+ → H2O2 + NAD+.
Cell Potential (E):
Defined as the difference between the electrode potentials of the cathode and anode.
E = ERHS - ELHS.
Standard Cell Potential (E°):
E° = E° RHS - E° LHS.
Positive cell potential (E > 0) indicates a spontaneous cell reaction.
Defined as the maximum amount of non-expansion work (Wmax = ΔG).
Max work possible if the process is reversible.
Zero-current cell potential (cell emf) is the voltage measured between electrodes with no current flowing.
Standard Reference:
SHE is assigned the zero value for electrode potential.
Configuration: H2 (1 atm) & Pt | H+ (aq).
E° for SHE = 0V at all temperatures.
Electrochemical Data:
Standard electrode potentials (E°) are tabulated for half-cell reactions.
E° indicates the zero-current cell potential relative to SHE.
Strong Electron Acceptors:
F2 + 2e- → 2F- (E° = +2.87V).
Cl2 + 2e- → 2Cl- (E° = +1.36V).
O2 + 4H+ + 4e- → 2H2O (E° = +1.23V).
Strong Electron Donors:
Na+ + e- → Na (E° = -2.71V).
Half-Cell Reactions:
O2 + 4H+ + 4e- → 2H2O (E° = +0.82V).
UQ + 2H+ + 2e- → UQH2 (E° = +0.11V).
NAD+ + H+ + 2e- → NADH (E° = -0.32V).
Relationship between electrochemistry and thermodynamics.
Gibbs Free Energy Calculation:
ΔG = Wmax = -nFE, where F = Faraday's constant (96485 C-mol⁻¹).
Gibbs Free Energy:
G° = -RT lnK.
ΔG = -nFE°
- lnK = (RT/E°).
Equation:
RT E = E° - (RT/nF) lnQ.
Applicable for half-cell reactions (reduction).
Equation:
RT E = (Rln[A]out/[A]in)/F.
Membrane potential related to concentrations of species inside and outside the membrane.
Title: Chemistry for Bioscientists I Section C13 Cell Potentials
Overall conclusion about the significance of cell potentials in biology.