What is Electrochemistry Class 12 Notes: Complete Guide for CBSE

Definition and Importance of Electrochemistry in Class 12 Chemistry

Electrochemistry is the study of chemical processes that cause electrons to move, generating electricity or using electricity to cause chemical changes. In Class 12 NCERT Chemistry, this chapter explains how redox reactions are involved in producing electrical energy and vice versa.

Understanding electrochemistry is important because:

• It explains batteries and fuel cells powering devices.
• It helps in industrial processes like electroplating.
• It forms the basis for analytical techniques such as potentiometry.

This chapter builds foundational knowledge essential for both theoretical understanding and practical applications in chemistry.

Redox Reactions: The Core of Electrochemistry

Redox reactions involve the transfer of electrons between substances. They are the heart of electrochemical processes.

• Oxidation is the loss of electrons.
• Reduction is the gain of electrons.

In electrochemistry, these reactions occur in two separate half-cells:

• Anode: Site of oxidation.
• Cathode: Site of reduction.

For example, in the reaction:

$$ Zn \rightarrow Zn^{2+} + 2e^- \quad (Oxidation) \\ Cu^{2+} + 2e^- \rightarrow Cu \quad (Reduction) $$

Electrons flow from zinc to copper, generating electrical current.

Electrochemical Cells: Galvanic and Electrolytic Cells Explained

Electrochemical cells convert chemical energy into electrical energy or vice versa. There are two main types:

Galvanic cells have two electrodes in electrolyte solutions connected by a salt bridge. Electrons flow spontaneously from anode to cathode.

Electrolytic cells require an external power source to drive the reaction, such as splitting water into hydrogen and oxygen gases.

Electrode Potential and Standard Electrode Potential

Electrode potential is the voltage developed at the electrode when it is in contact with its ions. It indicates the tendency of a species to gain or lose electrons.

• The Standard Electrode Potential ($E^\circ$) is measured under standard conditions (1 M concentration, 1 atm pressure, 25°C).

• The Standard Hydrogen Electrode (SHE) is the reference electrode with $E^\circ = 0$ V.

Electrode potentials help predict the direction of electron flow:

• The half-cell with higher $E^\circ$ acts as cathode (reduction).
• The half-cell with lower $E^\circ$ acts as anode (oxidation).

Example:

Electrons flow from zinc to copper in a Daniell cell.

Nernst Equation: Calculating Cell Potential Under Non-Standard Conditions

The Nernst equation allows calculation of the cell potential when conditions differ from standard:

$$ E = E^\circ - \frac{RT}{nF} \ln Q $$

Where:

• $E$ = cell potential at non-standard conditions
• $E^\circ$ = standard cell potential
• $R$ = gas constant (8.314 J/mol·K)
• $T$ = temperature in Kelvin
• $n$ = number of electrons transferred
• $F$ = Faraday’s constant (96485 C/mol)
• $Q$ = reaction quotient

At 25°C, the equation simplifies to:

$$ E = E^\circ - \frac{0.0591}{n} \log Q $$

Worked Example:

Calculate the cell potential for the reaction:

$$Zn + Cu^{2+} \rightarrow Zn^{2+} + Cu$$

Given:

• $E^\circ = 1.10$ V
• $[Cu^{2+}] = 0.01$ M
• $[Zn^{2+}] = 1$ M

Reaction quotient $Q = \frac{[Zn^{2+}]}{[Cu^{2+}]} = \frac{1}{0.01} = 100$

Number of electrons transferred $n=2$

$$ E = 1.10 - \frac{0.0591}{2} \log 100 = 1.10 - 0.0591 = 1.04 \text{ V} $$

Applications of Electrochemistry in Daily Life and Industry

Electrochemistry has many practical applications:

• Batteries and Cells: Power devices using galvanic cells (e.g., dry cells, lead-acid batteries).
• Electroplating: Depositing a layer of metal (silver, chromium) on objects to prevent corrosion or for decoration.
• Electrolysis: Used in extraction of metals like aluminium and in water splitting.
• Corrosion Prevention: Understanding electrochemical corrosion helps in protecting metals.
• Sensors and Fuel Cells: Electrochemical sensors detect gases; fuel cells generate clean energy.

These applications highlight the importance of mastering electrochemistry concepts for both exams and real-world understanding.