Masterton8e_PPT_CH17 Electrochemistry

Chapter 17: Electrochemistry

17.1 Oxidation-Reduction Reactions Revisited

  • Redox Reactions: Involves electron transfer between species.

  • Definition of oxidation and reduction:

    • Oxidation: Loss of electrons, increase in oxidation number.

    • Reduction: Gain of electrons, decrease in oxidation number.

  • Oxidizing Agent: Accepts electrons (causes oxidation).

  • Reducing Agent: Donates electrons (causes reduction).

17.2 Voltaic Cells

  • Voltaic Cell: Converts spontaneous redox reactions into electrical energy.

    • Anode: Site of oxidation (negative electrode).

    • Cathode: Site of reduction (positive electrode).

  • Electrons flow from anode to cathode through an external circuit.

17.3 Standard Voltages

  • Standard Cell Voltage (E°): Measured under standard conditions (1 M concentration, 1 atm pressure).

  • Cell voltage indicates the driving force for electrochemical reactions.

17.4 Relations between E°, ΔG°, and K

  • ΔG°: Standard free energy change which indicates spontaneity.

  • Relationship: ΔG° = -nFE°

    • n = moles of electrons transferred.

    • F = Faraday's constant.

  • If E° > 0: Spontaneous reaction (K > 1).

17.5 Effect of Concentration on Voltage

  • Voltage is affected by concentration changes:

    • Increase reactant concentration = Increase voltage.

    • Decrease reactant concentration = Decrease voltage.

17.6 Electrolytic Cells

  • Electrolytic Cell: Nonspontaneous reaction driven by external electric energy.

    • Used for electrolysis processes.

17.7 Commercial Cells

  • Types of electrochemical cells including:

    • Primary (non-rechargeable) cells e.g. alkaline batteries.

    • Secondary (rechargeable) cells e.g. lead-acid, lithium-ion batteries.

Key Concepts

  • Balancing Redox Reactions: Essential step in understanding redox chemistry.

    • Steps: Assign oxidation numbers, split into half-reactions, balance charges and mass.

  • Nernst Equation: Relationships between concentration and voltage in electrochemical reactions.

Experimental and Practical Applications

  • Electrolysis: Utilized to produce elements such as chlorine and hydrogen.

  • Fuel Cells: Efficient energy conversion methods generating electricity from hydrogen and oxygen reactions, producing only water as a byproduct.

Summary of Important Definitions

  • Oxidation: Loss of electrons or increase in oxidation state.

  • Reduction: Gain of electrons or decrease in oxidation state.

  • Voltaic Cell: Device generating electrical energy from spontaneous chemical reactions.

  • Electrolytic Cell: Device utilizing electrical energy to drive nonspontaneous reactions.