electrochemistry

• Electrolysis is the decomposition of a molten or aqueous ionic compound (an electrolyte) by passing an electric current through it, requiring a cathode (negative electrode) and an anode (positive electrode)
• The Faraday constant (F) is equal to the Avogadro constant (L) multiplied by the charge of an electron in coulombs (e): F = Le
• 1 faraday = 9.65 x 10^4 C mol^-1 (coulombs per mole)
• When the electrolyte is molten, cations move to the cathode and gain electrons to form atoms, while anions move towards the anode, lose electrons, and become atoms
• Inert electrodes used for electrolysis determine the product at the cathode based on the metal ions' position in the electrochemical series
• When using inert electrodes, oxygen is generally produced at the anode, but if concentrated chlorine ions are present, chlorine will form
• During electrolysis with non-inert electrodes, the same reaction occurs at the cathode, while atoms in the anode lose electrons to form ions in the electrolyte, resulting in a transfer of an element from the anode to the cathode
• The amount of charge passed during electrolysis can be calculated using the equations F=Le and number of coulombs = current x time (Q=It)
• To find the mass of silver liberated during the electrolysis of AgNO3, calculate the number of coulombs, use the cathode reaction Ag+ + e- → Ag, and apply the conversion factors
• To find the volume of hydrogen produced during the electrolysis of H2SO4 at room temperature and pressure, calculate the number of coulombs, use the cathode reaction 2H+ + 2e- → H2, and apply the conversion factors
• A half cell in electrochemistry contains an element in two oxidation states, establishing equilibrium between them on the surface of a solid
• Standard electrode potential (EӨ): the emf of a half cell compared with a hydrogen half cell under standard conditions
• Standard cell potential (EӨcell): the emf when two half cells are connected under standard conditions
• Emf (electromotive force) is the voltage when no current flows
• An equilibrium is set up on the surface of the platinum electrode between the hydrogen gas molecules and the hydrogen ions in solution: 2H​+​(aq) + 2e​-​ ⇋ H​2​(g)
• To measure standard electrode potentials, a closed circuit must be created with a salt bridge between two solutions and a wire connecting the two electrodes, allowing charge to flow
• The standard cell potential can be calculated by connecting two half cells with different electrode potentials, where the more positive E​Ө​ half cell gains electrons and the more negative E​Ө​ half cell releases electrons
• A reaction is feasible if the cell potential is positive; half cells with more negative electrode potentials are more likely to be oxidized and lose electrons
• The Nernst equation is used to calculate the electrode potential of a half cell when the concentration of aqueous ions changes, with the formula: E = E​Ө​ - (0.059/z) * log([reduced species]/[oxidised species])