Electrochemistry Lecture 2: Cell Representation and EMF

Introduction

• Lecture Topic: Electrochemistry
• Focus: Cell notations and EMF (Electromotive Force)

Review of Electrochemical Cells

• Galvanic Cell: Produces electricity through chemical reaction.
• Electrolytic Cell: Consumes electricity to drive non-spontaneous reactions.

Cell Representation

• Purpose: Simplify the representation of electrochemical cells without drawing diagrams.
• Key Elements:
  • Salt Bridge: Double line (||) in cell notation.
  • Anode Species: On the left side; oxidation occurs here.
  • Cathode Species: On the right side; reduction occurs here.

Cell Notations

• Anode Reaction: Oxidation (loss of electrons); e.g., Zn → Zn²⁺ + 2e⁻.
• Cathode Reaction: Reduction (gain of electrons); e.g., Cu²⁺ + 2e⁻ → Cu.
• Order: Ions first (inner side), then gases, and finally solid metals (outer side).

Types of Half Cells

1. Metal-Metal Ion Half Cell: Electrode metal in its ionic solution.
   • Example: Zinc in zinc sulfate solution.
2. Gas-Ion Half Cell: Gas, ionic solution, inert electrode (e.g., Pt).

Steps for Cell Representation

• Write ions first, then gases, and last solid electrode.
• Use a phase change line (|) to denote change from ions to gases or solids.
• If multiple ions, separate with commas.

Rules for Cell Notation

• Electrodes placed at extreme ends.
• Double line indicates a salt bridge.
• Sequence does not show direction of reaction.
• Oxidation at LHS (Anode), Reduction at RHS (Cathode).

Types of Half Cells

• Metal-Metal Ion Half Cell: E.g., Zn/Zn²⁺.
• Gas-Ion Half Cell: E.g., H₂/H⁺ involving inert electrodes.

Redox Reactions

• Redox: Combination of oxidation and reduction reactions.
• Redox Half Cell: Electrode reaction involving both oxidized and reduced ions.

EMF (Electromotive Force)

• Definition: Measure of a cell's ability to produce an electric current.
• Factors Affecting EMF:
  • Nature of chemical reaction.
  • Concentration of reactants/products.
  • Pressure of gases involved.
  • Temperature of the reaction.

Standard EMF

• SATP Conditions: Standard Ambient Temperature and Pressure
  • Concentration: 1 M
  • Temperature: 298 K
  • Pressure: 1 atm
• Standard EMF: Calculated under SATP conditions.

Calculation of EMF

• Formula: E⁰_cell = E⁰_cathode - E⁰_anode
• Positive EMF indicates spontaneous reactions.
• Negative EMF indicates non-spontaneous reactions.

Analyzing Cell Reactions

• Oxidation Potentials: Reverse of reduction potentials.
• Direction of Reaction: Indicated by the potential values.
  • Positive value means spontaneous in given direction.
  • Negative value means non-spontaneous.

Solving Problems

• Procedure:
  • Identify anode and cathode reactions.
  • Write down oxidation and reduction potentials.
  • Use EMF formula to calculate cell potential.

Conclusion

• EMF: Key to understanding spontaneity of reactions.
• Chemistry: Understanding concepts simplifies problem-solving.
• Encouragement: Find beauty in chemistry for better learning and results.