Electrochemistry

Introduction to Electrochemistry

Electrochemistry is the branch of chemistry that studies the interconversion of chemical and electrical energy. It is fundamentally concerned with the movement of electrons in redox (reduction-oxidation) reactions, which can be harnessed to generate electricity or drive non-spontaneous chemical changes.

• Electricity is the flow of electrons through a conductor.

• Redox reactions involve the transfer of electrons between chemical species.

Types of Electrochemical Cells

Electrochemical cells are devices that convert chemical energy into electrical energy or vice versa. They are classified based on the spontaneity of the redox reaction:

Electrode Potentials

Cell Potential and Electromotive Force (emf)

The cell potential (also called electromotive force, emf, or ) is the voltage produced by an electrochemical cell. It is measured in volts (V) and represents the driving force for electron flow from the anode to the cathode.

• Anode: Electrode where oxidation occurs.

• Cathode: Electrode where reduction occurs.

Cell Diagram Notation

A shorthand notation is used to represent electrochemical cells:

• Single vertical line (|): phase boundary between different states (solid, liquid, aqueous).

• Double vertical line (||): salt bridge separating the two half-cells.

• Example: Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s)

In this notation, the left side is the anode (oxidation), and the right side is the cathode (reduction).

Standard Electrode Potentials ()

The standard electrode potential () is a measure of the tendency of a chemical species to be reduced, measured under standard conditions (1 M concentration, 1 atm pressure, 25bC). The Standard Hydrogen Electrode (SHE) is assigned a potential of 0 V and serves as the reference.

• More positive values indicate a greater tendency to be reduced.

• More negative values indicate a greater tendency to be oxidized.

Calculating Standard Cell Potentials

The standard cell potential () is calculated as:

Where:

• = standard reduction potential of the cathode

• = standard reduction potential of the anode

Example: For the cell Zn(s) | Zn2+(aq) || Cl2(g) | Cl-(aq):

• Zn(s) → Zn2+(aq) + 2e- V

• Cl2(g) + 2e- → 2Cl-(aq) V

• V

Identifying Oxidation and Reduction

In a cell, the species with the higher (more positive) is reduced (cathode), and the species with the lower (more negative) $E^$ is oxidized (anode).

Effect of Concentration: The Nernst Equation

Nernst Equation

The Nernst equation relates the cell potential to the concentrations of the reactants and products:

• at 25bC

• Where = number of moles of electrons transferred, = reaction quotient

Example: For a cell with non-standard concentrations, use the Nernst equation to calculate the actual cell potential.

Relationship Between , , and

• at 25bC

• Where = Faraday constant ($96485R J/mol·K), = temperature in Kelvin, = equilibrium constant

Electrolysis

Electrolytic Cells

Electrolysis is the process of using electrical energy to drive a non-spontaneous chemical reaction. Electrolytic cells are used in various industrial processes, such as metal refining and electroplating.

• Anode is positive; cathode is negative.

• Example: Electrolysis of molten CaCl2 to produce calcium metal.

Faraday's Laws of Electrolysis

The amount of substance produced at each electrode during electrolysis is proportional to the quantity of electricity passed through the cell.

• = charge in coulombs (C)

• = current in amperes (A)

• = time in seconds (s)

• 1 Faraday () = 1 mole of electrons = $96485$ C

Steps for Quantitative Electrolysis Calculations

1. Calculate total charge:

2. Convert charge to moles of electrons:

3. Use stoichiometry to find moles of substance produced or consumed.

4. Convert moles to mass if required:

Example: Passing 0.452 A for 1.50 hours through molten CaCl2 produces 0.51 g of Ca metal.

Summary Table: Key Electrochemical Concepts

Additional info: Some equations and values (e.g., Nernst equation at 25bC) have been standardized for clarity. Examples and explanations have been expanded for completeness.