CM011 ELECTROCHEMISTRY

Electrochemical Principles

  • Electrochemistry: The study of the relationship between chemical reactions and electricity, emphasizing how reactions can produce electrical energy.

  • Electricity: Movement of electrons, fundamental for electrochemical processes.

  • Oxidation-Reduction (Redox) Reaction: Involves electron transfer between atoms. Includes oxidation (loss of electrons) and reduction (gain of electrons).

  • Oxidation Number: Indicates an atom's tendency to lose or gain electrons during reactions.

Types of Cells

  • Galvanic (Voltaic) Cells:

    • Generate electricity through spontaneous chemical reactions.

    • Composed of two electrodes (anode and cathode) in an electrolyte.

    • Anode is negative; cathode is positive.

    • Electrons flow from anode to cathode.

    • Redox reactions are spontaneous, producing electrical energy without external input.

    • Half-cells arranged in separate containers connected by a salt bridge.

  • Electrolytic Cells:

    • Convert electrical energy into chemical energy, facilitating non-spontaneous reactions.

    • Require external energy input to progress.

    • Both electrodes exist in the same container with the molten electrolyte.

    • Anode is positive; cathode is negative.

    • External battery supplies electrons, entering at the cathode and exiting at the anode.

Cell Functions and Laws

  • Concentration Cell: A cell where voltage is generated due to a difference in concentration.

  • Electrolytic Reaction: A process where electrical energy is used to drive a non-spontaneous chemical reaction.

  • Gibbs Free Energy Relation:

    • Formula: ΔG = -nFE

    • Implication: Spontaneous reactions (−ΔG) correspond to positive cell potential (+Ecell).

    • ΔG= -n F Ecell

    • n= number of electrons transferred

    • F= Faraday Constant = charge/ mol of e

    • (e charge x avogadro’s number)

    • (1.60 × 10 ^-19 C) (6.022 × 10 ²³)

    • = F = 96,485 C/mol

  • Faraday's Law of Electrolysis:

    • The mass of a substance deposited is directly proportional to the total electric charge (Coulombs) passed through the electrolyte.

  • Nernst Equation

Chemical Properties

  • Electrolyte: A substance that produces an electrically conducting solution when dissolved in a polar solvent like water.

  • Polar Molecules: Molecules with uneven charge distribution due to electronegativity differences.

  • Non-Polar Molecules: Molecules with an even charge distribution, lacking distinct positive or negative ends.

  • Standard Reduction Potentials: More positive values indicate a stronger tendency to attract electrons.

Chemical Reactions and Conditions

  • Corrosion Process: Occurs when dissimilar metals come into contact with an electrolyte, leading to oxidation reactions (e.g., saltwater).

  • Voltage Definition: The electric potential difference between two electrodes, measured as energy per unit charge.

  • Standard Potential (E°) Conditions:

    • Measured when solutes are at 1 M concentration, gases at 1 bar pressure, and solids are pure.

  • E°cell Favorability:

    • A positive E°cell indicates product-favored reactions, while a negative value suggests reactant favor