Graduate
  1. Physical Chemistry  1.1. Thermodynamics  1.1.1. Laws of Thermodynamics  1.1.2. Enthalpy and heat capacity  1.1.3. Entropy and free energy  1.1.4. Phase Equilibrium  1.1.5. Statistical thermodynamics  1.1.6. Thermodynamic cycle  1.1.7. Fugacity and activity  1.2. Quantum Chemistry  1.2.1. Principles of quantum mechanics  1.2.2. Schrödinger Equation  1.2.3. Particle in a box  1.2.4. Operators and eigenvalues  1.2.5. Atomic orbitals  1.2.6. Molecular orbital theory  1.2.7. Perturbation theory  1.2.8. Valence bond theory  1.2.9. Hybridization and chemical bonding  1.3. Chemical kinetics  1.3.1. Rate laws and reaction mechanisms  1.3.2. Collision theory  1.3.3. Transition state theory  1.3.4. Enzyme Kinetics  1.3.5. Chain Reactions and Polymerization  1.3.6. Photochemical reactions  1.4. Statistical mechanics  1.4.1. Partitioning functions  1.4.2. Molecular distribution functions  1.4.3. Boltzmann Distribution  1.4.4. Bose–Einstein and Fermi–Dirac statistics  1.5. Spectroscopy  1.5.1. Rotational Spectroscopy  1.5.2. Vibrational Spectroscopy  1.5.3. Electronic Spectroscopy  1.5.4. Nuclear magnetic resonance spectroscopy  1.5.5. Mass Spectrometry  1.5.6. Raman Spectroscopy  1.5.7. Electron paramagnetic resonance spectroscopy  1.6. Surface and colloidal chemistry  1.6.1. Absorption isotherm  1.6.2. Surface tension and wetting  1.6.3. Colloidal Stability  1.6.4. Catalysis  1.6.5. Emulsions and micelles  1.7. Electrochemistry  1.7.1. Nernst equation  1.7.2. Electrochemical cells  1.7.3. Conductivity and mobility  1.7.4. War  1.7.5. Fuel cells  1.7.6. Electrolysis
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic reactions  2.2. Spectroscopy and structural determination  2.2.1. UV-Vis Spectroscopy  2.2.2. IR Spectroscopy  2.2.3. NMR Spectroscopy  2.2.4. Mass Spectrometry  2.2.5. X-ray crystallography  2.3. Stereoscopic  2.3.1. Chirality and optical activity  2.3.2. Structural analysis  2.3.3. Geometrical isomerism  2.3.4. Dynamic Stereochemistry  2.4. Organometallic Chemistry  2.4.1. Organolithium and organomagnesium reagents  2.4.2. Palladium-catalyzed cross-coupling reactions  2.4.3. Transition Metal Complexes  2.4.4. Metal–carbon bond  2.5. Polymer chemistry  2.5.1. Polymerization mechanism  2.5.2. Polymer Characteristics  2.5.3. Biodegradable Polymer  2.5.4. Conducting polymer  2.5.5. Supramolecular polymers  2.6. Medicinal chemistry  2.6.1. Drug design and development  2.6.2. Pharmacokinetics and pharmacodynamics  2.6.3. Structure-activity relationships  2.6.4. Molecular docking and drug screening
  3. Inorganic chemistry  3.1. Coordination chemistry  3.1.1. Crystal field theory  3.1.2. Ligand field theory  3.1.3. Spectrochemical Series  3.1.4. Chelation and stability  3.2. Organometallic Chemistry  3.2.1. Metal Carbonyls  3.2.2. Catalysis by organometallic complexes  3.2.3. Metallocenes  3.3. Bio-inorganic chemistry  3.3.1. Metalloproteins and enzymes  3.3.2. The role of metals in biological systems  3.3.3. Metal ion transport and storage  3.4. Solid state chemistry  3.4.1. Crystal Structures  3.4.2. Band theory of solids  3.4.3. Superconductors  3.4.4. Defects in the crystal  3.5. Lanthanides and Actinides  3.5.1. Electronic configuration in lanthanides and actinides  3.5.2. Coordination chemistry of the lanthanides  3.5.3. Magnetic Properties of Lanthanides
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.2. Spectroscopic Techniques  4.2.1. Atomic absorption spectroscopy  4.2.2. X-ray diffraction  4.2.3. Inductively coupled plasma spectroscopy  4.3. Electroanalytical methods  4.3.1. Potentiometry  4.3.2. Voltammetry  4.3.3. Colometry  4.4. Mass Spectrometry  4.4.1. Ionization Technique  4.4.2. Fragmentation Pattern  4.5. Chemometrics  4.5.1. Multidisciplinary analysis  4.5.2. Machine Learning in Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.1.1. Force fields and energy minimization  5.1.2. Monte Carlo simulation in molecular dynamics simulations  5.2. Quantum chemical methods  5.2.1. Hartree–Fock theory  5.2.2. Density functional theory  5.2.3. Semi-empirical methods  5.3. Computational drug design  5.3.1. Molecular Docking  5.3.2. QSAR Modeling  5.3.3. Virtual Screening
  6. Biochemistry  6.1. Enzyme Kinetics  6.1.1. Michaelis-Menten kinetics  6.1.2. Inhibition mechanism  6.2. Metabolism and Bioenergetics  6.2.1. Glycolysis  6.2.2. Citric acid cycle  6.2.3. Electron transport chain  6.3. molecular Biology  6.3.1. DNA replication and repair  6.3.2. Protein synthesis  6.3.3. Gene Regulation  6.4. Structural Biochemistry  6.4.1. Protein Folding  6.4.2. Membrane Biophysics
  7. Environmental Chemistry  7.1. Atmospheric Chemistry  7.1.1. Greenhouse gases  7.1.2. Ozone depletion  7.1.3. Air pollutants and smoke  7.2. Water Chemistry  7.2.1. pH and water hardness  7.2.2. Wastewater treatment  7.2.3. Aquatic Chemistry  7.3. Soil Chemistry  7.3.1. Heavy metal contamination  7.3.2. Soil pH and Buffering  7.3.3. Nutrient cycling  7.4. Toxicology and Chemical Safety  7.4.1. Toxicokinetics  7.4.2. Risk Assessment in Toxicology and Chemical Safety in Environmental Chemistry  7.4.3. Effects of pollutants on the environment

Graduate → Physical Chemistry → Chemical kinetics ↓


Chain Reactions and Polymerization


Chemical kinetics focuses on understanding the rates of chemical reactions and the steps in which they occur. This knowledge helps us understand how molecules interact, transform, and form products. Two important processes often discussed in chemical kinetics are chain reactions and polymerization. Both involve complex sequences of reactions, although they occur under different contexts and applications.

Chain reactions: A detailed overview

Chain reactions are sequences of reactions where a reactive intermediate, often a radical, facilitates the transformation of reactants into products through a series of propagation steps. These reactions can proceed very quickly and sometimes produce explosive results.

Initial stage

The first step in a chain reaction is the initiation step. During this step, reactive intermediates are produced, usually through thermal decomposition, photolysis, or reactions with other chemicals.

Example:

Consider the chlorine and hydrogen reaction:

Cl 2 → 2 Cl•

Here, chlorine gas absorbs energy (e.g., UV light) to form two chlorine radicals (Cl•).

Proliferation phase

In propagation steps, intermediate substances react with stable molecules to form new intermediate substances and products. Propagation usually involves the conversion of initial reactants into final products.

Example:

Continuing the chlorine and hydrogen reaction, chain propagation involves two main steps:

1. Cl• + H 2 → HCl + H• 2. H• + Cl 2 → HCl + Cl•

These steps recycle the reactive intermediates H• and Cl•, allowing the reaction to continue.

Termination phase

Chain reactions do not continue indefinitely. Termination occurs when the reactive intermediates combine to form stable molecules, leaving the intermediates in short supply.

Example:

Termination can be as follows:

Cl• + Cl• → Cl 2 H• + H• → H 2

These reactions remove radicals from the system, thereby inhibiting further reactions.

Visual representation

+------------------+
| Initiation       |
+------------------+
⬇
1. Cl 2 → 2 Cl•
+------------------+
| Propagation      |
+------------------+
⬇
2. Cl• + H 2 → HCl + H•
3. H• + Cl 2 → HCl + Cl•
+------------------+
| Termination      |
+------------------+
⬇
4. Cl• + Cl• → Cl 2
5. H• + H• → H 2

Polymerization reactions

Polymerization involves linking monomer units into long, repeating chains known as polymers. These reactions are important in the manufacture of many kinds of materials, from plastics to synthetic fibers.

Addition polymerization

Addition or chain-growth polymerization typically involves unsaturated monomers (such as alkenes) that form polymers through initiation, propagation, and termination steps.

Initiation of polymerization

A radical initiator initiates the polymerization by reacting with a monomer unit, forming a radical that can propagate the reaction.

Example:

Consider the polymerization of polyethylene from ethylene:

Initiator → Initiator•
Initiator• + CH 2 =CH 2 → Initiator-CH 2 -CH 2 •

The initiator radical attacks the double bond of ethylene, producing a new radical.

Diffusion in polymerization

During propagation, the end of the active chain adds more monomers, causing the polymer chain to grow.

Example:

This series progresses as follows:

Initiator-CH 2 -CH 2 • + CH 2 =CH 2 → Initiator-(CH 2 -CH 2 ) 2 •

This process continues, consuming more ethylene molecules and extending the polymer chain.

Termination of polymerization

Termination in addition polymerization may occur as a result of addition or disproportionation events.

Example:

Two possible scenarios of termination:

1. Combination: Initiator-(CH 2 -CH 2 ) n • + Initiator-(CH 2 -CH 2 ) m • → Initiator-(CH 2 -CH 2 ) n+m -Initiator
2. Disproportionation: Initiator-(CH 2 -CH 2 ) n • + Initiator-(CH 2 -CH 2 ) m • → Terminated polymer

This stops the polymerization process.

Step-growth polymerization

In contrast to addition polymerization, step-growth polymerization involves the random reaction of bifunctional or multifunctional monomers.

Example:

Nylon production via polycondensation of hexamethylenediamine and adipic acid:

NH 2 -(CH 2 ) 6 -NH 2 + HOOC-(CH 2 ) 4 -COOH → [-NH-(CH 2 ) 6 -NH-CO-(CH 2 ) 4 -COO-] n + (2n - 1) H 2 O

This polymerization occurs through the formation and expansion of different molecular sizes until they become a polymer.

Visual representation

+----------------------+
| Initiation Phase     |
+----------------------+
⬇
Initiator → Initiator•
Initiator• + Monomer → Initiator-Monomer•
+----------------------+
| Propagation Phase    |
+----------------------+
⬇
Initiator-Monomer• + Monomer → Initiator-(Monomer) n •
+----------------------+
| Termination Phase    |
+----------------------+
⬇
Combination or Disproportionation

Importance of chain reactions and polymerisation

Understanding chain reactions and polymerization is important in a variety of industrial applications. Chain reactions are fundamental in combustion processes, where control is crucial to ensure safety and efficiency. In the field of polymers, mastering polymerization techniques allows the properties of plastics and resins to be optimized for specific uses, from everyday materials to advanced technological applications.

Textual examples

Consider the automotive industry, which relies heavily on polymerization. Tires, plastic parts, and coatings are the products of well-designed polymerization reactions. Chain reactions are also important in internal combustion engines, where controlled explosive reactions of hydrocarbons power vehicles.

Conclusion

Careful balancing of initiation, propagation, and termination steps ensures efficient and controlled release of energy or formation of materials in both chain reactions and polymerization. Advances in this area facilitate innovations in polymer science and sustainable chemistry.


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