General Electrochemistry

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Electrochemistry, in a sense, is electron movement. The study of electrochemistry is what makes the computer/tablet/phone you are looking at this website possible.

Vocabulary/Things to Remember

  • In this we consider redox reactions: we have an oxidation and a reduction part of our reaction.
  • In oxidation, we lose electrons whereas in reduction we gain electrons (OIL RIG: Oxidation Is Loss; Reduction Is Gain).
  • Half-reaction: shows the independent oxidation or reduction reactions
  • Balancing Redox Reactions:
    1. atoms and charges must balance!
    2. Steps:
      1. Split into half-reactions
      2. for each half-reaction
        1. balance non-hydrogen or oxygen atoms and electrons
      3. Balance oxygens atoms with $H_2 O$
      4. Balance hydrogens with $H^+$
      5. Check atoms and charges
      6. Make electrons in each half-reaction equal and add them together
        1. You might wonder why the number of electrons is important
          1. The potential we measure will depend on the number of electrons in the redox process
  • Electrochemical Cells: we isolate the reduction and the oxidation in separate cells
    • this forces a path that the electrons have to follow
    • these are connected by a salt bride which completes the circuit but keeps the half-reaction separate
  • Potential ($E$): measure tendency for a reaction to move towards equilibrium
    • positive potential: spontaneous; favorable; electrons flow from anode to cathode
    • negative potential: electrolytic cell
  • Current ($I$): opposite direction of flow of electron
  • Reactions will proceed to equilibrium
  • Standard Reduction Potential ($E^{\circ}$): this is the electrode potential compared to a standard (usually the Standard Hydrogen Electrode)

Types of Cells

  • Galvanic Cell: proceeds on its own
    • favorable reaction
    • electrons will flow from anode to cathode
    • store energy
    • Here is a video that will help (have fun!): “You Start at the Anode”
  • Electrolytic Cell:
    • requires external energy to move electrons against potential
    • electrons flow from cathode to anode
    • i.e. recharging a battery
  • Reversible Cell:
    • these cells can act as a galvanic and electrolytic cell
    • i.e. car battery
  • Irreversible Cell:
    • can only act as a galvanic cell
    • changing direction will cause a different half-reaction to occur

Equations

  • $\Delta G = -RT \ln{K}$
  • $\Delta G = – nFE_{cell}$
    • $n$ = # of electrons
    • $F$: Faraday’s constant
  • $E_{cell}^{\circ} = E_{cathode}^{\circ} – E_{anode}^{\circ}$
    • always work in terms of reduction equations so you can pull the values straight from the table
  • $E_{cell}$ @ equilibrium = 0
  • shorthand notation:
    • plus right rule: anode(oxidation) || cathode (reduction)

solid anode | anode (next phase,concentration) || cathode (next phase) | solid cathode

    • | : phase boundary; use every time you change phases
    • || : salt bridge

Problem Solving: Half Cell (~3 minutes)