Electrochemistry Notes

Introduction

Electrochemistry is a branch of chemistry that deals with the relationship between electrical energy and chemical changes. It encompasses the study of both spontaneous and non-spontaneous processes where oxidation and reduction reactions occur. This topic is crucial for the NEET Chemistry syllabus as it forms the basis for understanding various biological, industrial, and environmental processes.

Oxidation and Reduction Reactions

Oxidation

Oxidation is the loss of electrons by a species. It occurs when an element or compound increases its oxidation state.

• Example: In the reaction $ \text{Fe} \rightarrow \text{Fe}^{2+} + 2e^- $, iron (Fe) is oxidized to iron (II) ion ($\text{Fe}^{2+}$).

Reduction

Reduction is the gain of electrons by a species. It involves a decrease in the oxidation state.

• Example: In the reaction $ \text{Cu}^{2+} + 2e^- \rightarrow \text{Cu} $, copper (II) ion ($\text{Cu}^{2+}$) is reduced to copper (Cu).

Electrochemical Cells

Galvanic (Voltaic) Cells

Galvanic cells convert chemical energy into electrical energy through spontaneous redox reactions.

• Components:
  • Anode: The electrode where oxidation occurs.
  • Cathode: The electrode where reduction occurs.
  • Salt Bridge: Maintains electrical neutrality by allowing the flow of ions.
• Example: Daniell Cell
  • Anode Reaction: $ \text{Zn} \rightarrow \text{Zn}^{2+} + 2e^- $
  • Cathode Reaction: $ \text{Cu}^{2+} + 2e^- \rightarrow \text{Cu} $

Electrolytic Cells

Electrolytic cells use electrical energy to drive non-spontaneous chemical reactions.

• Components:
  • Anode: The electrode where oxidation occurs (positive terminal).
  • Cathode: The electrode where reduction occurs (negative terminal).
• Example: Electrolysis of water
  • Anode Reaction: $ 2\text{H}_2\text{O} \rightarrow \text{O}_2 + 4\text{H}^+ + 4e^- $
  • Cathode Reaction: $ 4\text{H}^+ + 4e^- \rightarrow 2\text{H}_2 $

Standard Electrode Potential

Definition

The standard electrode potential ($E^\circ$) is the measure of the individual potential of a reversible electrode at standard state, which is $1$ M concentration for solutions, $1$ atm pressure for gases, and pure solids or liquids.

Standard Hydrogen Electrode (SHE)

• Reaction: $ 2\text{H}^+ + 2e^- \rightarrow \text{H}_2 $
• Potential: $E^\circ = 0.00 \text{ V}$

Calculating Cell Potential

The cell potential ($E^\circ_{\text{cell}}$) is calculated using the standard electrode potentials of the cathode and anode. $$ E^\circ_{\text{cell}} = E^\circ_{\text{cathode}} - E^\circ_{\text{anode}} $$

Nernst Equation

The Nernst equation relates the cell potential to the standard electrode potential and the reaction quotient ($Q$). $$ E_{\text{cell}} = E^\circ_{\text{cell}} - \frac{RT}{nF} \ln Q $$ Where:

• $R$ is the gas constant ($8.314 \text{ J mol}^{-1} \text{ K}^{-1}$),
• $T$ is the temperature in Kelvin,
• $n$ is the number of moles of electrons,
• $F$ is the Faraday constant ($96485 \text{ C mol}^{-1}$).

Electrolysis and Faraday's Laws

Faraday's First Law

The mass of a substance deposited or liberated at an electrode is directly proportional to the quantity of electricity passed. $$ m = Z \cdot Q $$ Where:

• $m$ is the mass of the substance,
• $Z$ is the electrochemical equivalent,
• $Q$ is the charge.

Faraday's Second Law

The mass of substances deposited or liberated by the same quantity of electricity is proportional to their equivalent weights.

Applications of Electrochemistry

Batteries

• Primary Batteries: Non-rechargeable (e.g., dry cell, alkaline battery).
• Secondary Batteries: Rechargeable (e.g., lead-acid battery, lithium-ion battery).

Corrosion

Corrosion is the deterioration of metals due to redox reactions with environmental elements.

• Prevention: Coating, galvanization, and using sacrificial anodes.

Electroplating

The process of depositing a layer of a metal onto a surface using electrolysis.

• Example: Gold plating on jewelry.

Conclusion

Electrochemistry is a vast and intricate field that bridges the gap between chemical reactions and electrical energy. Mastering the fundamental concepts, such as redox reactions, electrochemical cells, electrode potentials, and Faraday's laws, is crucial for excelling in NEET Chemistry. Remember to practice problems and relate theoretical knowledge to practical applications to enhance your understanding.

[Image: Diagram of a Daniell Cell with labeled anode, cathode, salt bridge, and direction of electron flow]

Happy studying!