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 ↓


Thermodynamics


Thermodynamics is a fundamental branch of physical chemistry that deals with the principles governing energy and its transformations. This field provides us with tools to predict the direction of processes at the macroscopic level, irrespective of the microscopic details of matter. Here we will study thermodynamics in depth, cover its basic concepts and principles, and provide illustrative examples to enhance understanding.

Basic concepts of thermodynamics

System and environment

A central concept in thermodynamics is the definition of a system and its surroundings. The system refers to the part of the universe we are interested in studying, while the surroundings are everything else. Systems can be classified into three types:

  • Open system: can exchange energy and matter with the surrounding environment. For example, an open beaker filled with water.
  • Closed system: It can exchange energy but not matter with the surrounding environment. For example, a sealed container with a piston moving at a constant temperature.
  • Isolated system: cannot exchange energy or matter with the surrounding environment. For example, an insulated thermos bottle.

State function and state variables

The properties of a system can be described using state variables, which depend only on the current state of the system. Examples include pressure (P), volume (V), temperature (T), and internal energy (U). These are also known as state functions because their values depend only on the state of the system, not on how the system reached that state.

Laws of thermodynamics

First law of thermodynamics

The first law of thermodynamics is the statement of conservation of energy. It states that energy cannot be created or destroyed, only transformed or transferred. Mathematically, it is expressed as:

        ΔU = Q – W

where ΔU is the change in internal energy, Q is the heat added to the system, and W is the work done by the system.

For example, consider a gas enclosed in a piston. If heat is added to the gas, this can cause the gas to expand, doing work on the piston.

Piston Gas

As the piston moves upward, it does work on the surroundings. The energy balance will look as described in the equation above.

Second law of thermodynamics

The second law of thermodynamics introduces the concept of entropy, which is a measure of disorder in a system. It states that the entropy of an isolated system always increases over time. It can be formulated as follows:

        ΔS ≥ 0

where ΔS is the change in entropy. In real processes, energy tends to dissipate, causing entropy to increase.

Consider mixing two gases, A and B, in an isolated system. Initially, the gases are separated by a partition. Once the partition is removed, the gases mix, moving toward a state of greater disorder (higher entropy).

Third law of thermodynamics

The third law of thermodynamics states that as the temperature of a system approaches absolute zero (0 Kelvin), the entropy of a perfectly ordered crystalline substance approaches zero. This law implies that it is impossible to reach absolute zero in a finite number of steps.

Thermodynamic processes

Isothermal process

In an isothermal process, the temperature of the system remains constant. A common example is when a gas is slowly compressed in a piston, exchanging heat with the surroundings and maintaining a constant temperature.

        q = w

In isothermal expansion or compression, the work done by or on the system is equal to the heat exchanged.

Adiabatic process

Adiabatic process occurs without heat exchange with the surroundings. During compression or expansion in an adiabatic process, the temperature of the system will change. The relationship between the variables is:

        PV γ = const

where γ is the adiabatic index, given by the ratio of heat capacities (Cp/Cv).

Isobaric and isochoric processes

Isobaric processes occur at constant pressure, while isochoric processes occur at constant volume. The relation for isochoric process is:

        w = 0

Since there is no change in volume, no work is done in the isochoric process.

Free energy and equilibrium

Gibbs free energy

The Gibbs free energy (G) is important for predicting the spontaneity of processes at constant pressure and temperature. The change in Gibbs free energy is given by:

        ΔG = ΔH – TΔS

Where ΔH is the change in enthalpy and ΔS is the change in entropy.

A process is spontaneous if:

        ΔG < 0

At equilibrium, ΔG is zero, that is, there is no net change.

Chemical equilibrium

In chemical reactions, thermodynamics can predict the state of equilibrium using the reaction quotient Q and the equilibrium constant K If Q < K, the reaction proceeds forward; if Q > K, the reaction regresses until Q = K at equilibrium.

Applications of thermodynamics

Engine efficiency

Thermodynamics is helpful in understanding the efficiency of engines, such as the Carnot engine. The efficiency of a Carnot engine operating between two thermal reservoirs is given by:

        Efficiency = 1 – (Tc/Th)

where Tc and Th are the absolute temperatures of the cold and hot reservoirs, respectively.

Refrigeration

The principles of thermodynamics also apply to refrigeration cycles, where heat is removed from the cooled space into the surrounding environment. The coefficient of performance (COP) is a measure of efficiency in heat pumps and refrigerators.

These few examples illustrate the wide range of applications and principles underlying thermodynamics in physical chemistry. Through these concepts, chemists can better understand the energy barriers and potentials that govern chemical reactions, phase changes, and all real-world processes.


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Thermodynamics

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