Physical Chemistry sangeetha maam

MODULE 2: PHYSICAL CHEMISTRY

Electrochemistry

• Electrode Potential:

  • Electrodes are crucial for measuring the tendency of a substance to lose or gain electrons.

  • Standard Electrode Potential: Measured against the standard hydrogen electrode (SHE), assigned a value of 0 volts.

• Electrolytic Cell:

  • Converts electrical energy into chemical energy.

  • Redox reactions are non-spontaneous; electrical energy is supplied to initiate reactions.

  • Both electrodes are in the same container with molten electrolyte solution.

  • The anode is positive (oxidation occurs) and the cathode is negative (reduction occurs).

• Electrochemical Cell:

  • Converts chemical energy into electrical energy.

  • Redox reactions are spontaneous; set up in separate containers connected by a salt bridge.

  • The anode is negative (oxidation) and the cathode is positive (reduction).

  • Example: Zinc anode and copper cathode configuration.

Thermodynamics

• First Law of Thermodynamics: Energy conservation principle, energy transformation allows change in form but not creation or destruction.

• Second Law of Thermodynamics: Entropy will always increase in a system; energy transfer is not 100% efficient.

• Enthalpy: Total energy content of a system at constant pressure; defined as H = U + PV. Change in enthalpy, ∆H, is equal to heat absorbed by the system.

• Entropy: Measure of disorder in a system; major influence on spontaneity and reversibility.

Chemical Kinetics

• Rate of Reaction: How fast a reactant is converted to products; measured as the change in concentration over time.

• Molecularity: Refers to the number of molecules involved in a reaction step.

  • Unimolecular (one), Bimolecular (two), Termolecular (three).

• Arrhenius Equation: Describes how the rate constant (k) depends on temperature (T) and activation energy (Ea).

• Activation Energy: This is the energy barrier that must be overcome for a chemical reaction to occur.

Nernst Equation

• Provides a way to calculate the potential of a cell under non-standard conditions; derived from the relationship between free energy, electrode potential, and concentration.

• Nernst Equation: E_cell = E°_cell - (RT/nF) ln(Q) --> describes potential dependent on concentration.

Biological Standard Potential

• Reflects standard reduction potentials under biological conditions (pH 7, 37°C). Helps in understanding biochemical reactions.

Experimental Methods

• Calomel Electrode: Common reference standard electrode with precision; involves mercury and calomel (Hg2Cl2).

• Standard Hydrogen Electrode: Used as a reference with defined properties; crucial for electrochemical measurements.