PHD
  1. Inorganic chemistry  1.1. Coordination chemistry  1.1.1. Ligand field theory  1.1.2. Crystal field theory  1.1.3. Molecular Orbital Theory for Coordination Compounds  1.1.4. Stability of Coordination Compounds  1.1.5. Electronic spectra of coordination compounds  1.1.6. Isomerism in Coordination Compounds  1.1.7. Kinetics and mechanism of coordination reactions  1.2. Organometallic Chemistry  1.2.1. Metal Carbonyls  1.2.2. Metal alkyl and aryl  1.2.3. Fischer and Schrock carbonaceans  1.2.4. Oxidative Addition and Reductive Elimination  1.2.5. Metal Hydrides  1.2.6. Catalysis by organometallic compounds  1.2.7. Metallocenes and Sandwich Complexes  1.2.8. CH activation  1.3. Solid state chemistry  1.3.1. Crystal structures and lattices  1.3.2. Band theory and electrical properties  1.3.3. Defects in the crystal  1.3.4. Synthesis of solid state materials  1.3.5. Magnetic and optical properties of solids  1.3.6. Superconductivity  1.3.7. Solid state ionics  1.4. Bio-inorganic chemistry  1.4.1. Metalloproteins and enzymes  1.4.2. Metal ion transport and storage  1.4.3. The role of metals in medicine  1.4.4. Bioinspired catalysis  1.4.5. Metal–DNA interactions  1.4.6. Metal Complexes in Medical Science  1.5. Lanthanides and Actinides  1.5.1. Electronic configuration and oxidation states in lanthanides and actinides  1.5.2. Spectral and Magnetic Properties in Lanthanides and Actinides  1.5.3. Separation and Extraction of Lanthanides and Actinides  1.5.4. Coordination chemistry of f-block elements  1.6. Main Group Chemistry  1.6.1. Chemistry of boron compounds  1.6.2. Chemistry of Silicon and Germanium Compounds  1.6.3. Chemistry of Phosphorus and Sulfur Compounds  1.6.4. Organosilicon chemistry  1.6.5. Noble Gas Chemistry
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition and substitution reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic Reactions  2.1.7. Photochemical reactions  2.2. Stereoscopic  2.2.1. Chirality and optical activity  2.2.2. Structural analysis  2.2.3. Stereoelectronic effects  2.2.4. Asymmetric synthesis  2.2.5. Dynamic Stereochemistry  2.3. Organometallic Chemistry in Organic Synthesis  2.3.1. Organolithium and organomagnesium reagents  2.3.2. Transition metal catalyzed coupling reactions  2.3.3. Palladium-catalyzed reactions  2.3.4. Olefin Metathesis  2.3.5. Gold and silver catalysis  2.4. Natural products chemistry  2.4.1. Alkaloids and terpenoids  2.4.2. Steroids and Flavonoids  2.4.3. Total synthesis of natural products  2.4.4. Biosynthesis of natural products  2.5. Supramolecular Chemistry  2.5.1. Host-Guest Chemistry  2.5.2. Self-assembly and molecular recognition  2.5.3. Supramolecular Catalysis  2.5.4. Molecular Machines
  3. Physical Chemistry  3.1. Thermodynamics  3.1.1. Laws of Thermodynamics  3.1.2. Chemical Potential and Equilibrium  3.1.3. Statistical thermodynamics  3.1.4. Non-equilibrium thermodynamics  3.2. Quantum Chemistry  3.2.1. Schrödinger equation and its applications  3.2.2. Molecular orbital theory  3.2.3. Density functional theory  3.2.4. Post-Hartree–Fock methods  3.3. Chemical kinetics  3.3.1. Reaction rate theory  3.3.2. Mechanism and rate laws  3.3.3. Catalysis and enzyme kinetics  3.3.4. Reaction dynamics  3.4. Spectroscopy and molecular structure  3.4.1. Infrared Spectroscopy  3.4.2. UV-visible spectroscopy  3.4.3. Nuclear Magnetic Resonance Spectroscopy  3.4.4. Mass Spectrometry  3.4.5. Raman Spectroscopy  3.5. Surface and Colloid Chemistry  3.5.1. Absorption and Catalysis  3.5.2. Surfactants and micelles  3.5.3. Colloidal Stability  3.5.4. Nanomaterials and Interfaces
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.1.4. Ion Chromatography  4.2. Electroanalytical techniques  4.2.1. Voltammetry and Polarography  4.2.2. Conductometry and potentiometry  4.2.3. Colometry  4.3. Spectroscopic Methods  4.3.1. Atomic absorption spectroscopy  4.3.2. Fluorescence Spectroscopy  4.3.3. X-ray diffraction  4.3.4. Electron paramagnetic resonance spectroscopy  4.4. Chemometrics  4.4.1. Data processing and statistical methods  4.4.2. Multidisciplinary analysis  4.4.3. Machine Learning in Analytical Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.2. Quantum chemistry methods  5.3. Computational drug design  5.4. Machine Learning in Chemistry  5.5. Ab initio molecular dynamics
  6. Biophysics and Medicinal Chemistry  6.1. Drug discovery and design  6.2. Enzyme kinetics and inhibition  6.3. Chemical biology approach  6.4. Protein-ligand interactions  6.5. Bioorthogonal chemistry
  7. Materials chemistry  7.1. Polymer chemistry  7.1.1. Polymerization mechanism  7.1.2. Functional Polymers  7.1.3. Biodegradable Polymer  7.1.4. Conducting and semiconducting polymers  7.2. Nano Chemistry  7.2.1. Nanoparticles and nanostructures  7.2.2. Carbon-based nanomaterials  7.2.3. Quantum dots  7.3. Energy and Environmental Chemistry  7.3.1. Battery and Fuel Cell Chemistry  7.3.2. Green chemistry and sustainable materials  7.3.3. Photocatalysis

PHD → Physical Chemistry → Chemical kinetics ↓


Reaction rate theory


The study of reaction rates in chemical kinetics is fundamental to understanding how chemical reactions occur and proceed. Reaction rate theories aim to explain the velocities or rates at which chemical reactions occur. In physical chemistry, these theories provide information about the transitions from reactants to products and help predict reaction kinetics under various conditions.

Importance of reaction rate theories

Reaction rate theories are important because they allow chemists to predict the speed of a reaction, which is essential in industrial processes, pharmacology, and environmental science. By understanding these theories, one can control reaction conditions to optimize the yield of desired products. In addition, they provide a molecular-level understanding of reaction mechanisms and energy changes.

Basic concepts in reaction rate

A chemical reaction occurs when reactants change into products. The rate of this change is the reaction rate, usually expressed as the change in concentration of the reactant or product per unit time. The general form of the reaction rate can be given as:

        Rate = - (d[R]/dt) = (d[P]/dt)

where [R] and [P] are the concentrations of reactants and products, respectively.

Factors affecting the reaction rate

Several factors affect the reaction rate:

  • Concentration of reactants: Generally, higher concentration of reactants leads to higher rate of reaction.
  • Temperature: Increasing the temperature usually increases the reaction rate.
  • Presence of a catalyst: Catalysts lower the activation energy, and increase the reaction rate without being consumed.
  • Surface area: For reactions involving solids, a larger surface area can speed up the reaction.

Collision theory

Collision theory is one of the simplest models to explain reaction kinetics. It assumes that for a reaction to occur, reactant molecules must collide with sufficient energy and in the proper orientation. This energy threshold is called the activation energy (E_a).

Reactant A Reactant B Proper Orientation enough energy

According to collision theory, the reaction rate is proportional to the number of successful collisions. However, it does not take into account all the phenomena observed in chemical reactions.

Transition state theory

Transition state theory (TST), also known as activated complex theory, provides a more detailed approach than collision theory. It suggests that a transient intermediate, known as the transition state or activated complex, is formed during the reaction. The energy required to reach this transition state from the reactants is the activation energy.

Reactants Products Transition state Activation energy, E_a

Transition state theory takes into account the energy barrier that must be overcome to transform reactants into products. The reaction rate can be described by the Arrhenius equation:

        k = a * exp(-E_a / (r * t))

where k is the rate constant, A is the pre-exponential factor, R is the gas constant, and T is the temperature in Kelvin.

Arrhenius equation and temperature dependence

The Arrhenius equation provides a relationship between the rate constant (k) and temperature by introducing the concept of activation energy. This helps chemists understand how reaction rates change with temperature, which is particularly useful in predicting and controlling reactions.

K versus 1/T Low T High T

Potential energy surface

In complex reactions, potential energy surfaces (PES) depict the energy landscape of a chemical reaction. They depict the energy changes as molecules approach, form a transition state, and transform into products. PES provide a visual and mathematical tool for understanding how reactions proceed along different pathways.

Reactants Products Transition state

A practical example: the Haber process

Consider the Haber process for the synthesis of ammonia, where nitrogen and hydrogen gases react:

        N₂(g) + 3H₂(g) → 2NH₃(g)

This reaction is catalyzed by iron at high temperature and pressure. Understanding reaction rate principles helps optimize conditions, increasing efficiency and yield.

Conclusion

Reaction rate theories are invaluable tools for chemists and chemical engineers, providing a deeper understanding of how reactions occur and how to control them. From basic collision theory to more complex transition state theory and potential energy surfaces, these theories explain the microscopic phenomena that govern macroscopic observations. By applying these concepts, one can design and optimize reactions for a variety of applications, from industrial processes to biological systems.


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Reaction rate theory

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