Tag: GATE Chemistry

Physical Chemistry · Applied The Ellingham Diagram: Thermodynamics Deciding an Industrial Process A single plot that answers which reducing agent will work, and at what temperature, for any metal oxide. BSc & MSc · Physical Chemistry · Concept The short answer: The diagram plots the standard free energy of oxide formation against temperature. A metal whose line lies lower can reduce the oxide of one whose line lies higher. Most lines slope upward because forming a solid oxide consumes gas, but the carbon monoxide line slopes downward, which is why carbon becomes a universal reducing agent at high temperature. What…

Determining Polymer Molar Mass: Which Average and Which Method

September 16, 2026

Physical Chemistry · Macromolecules Determining Polymer Molar Mass: Which Average and Which Method A polymer has no single molar mass, so the method you choose determines which average you get — and the two can differ substantially. BSc & MSc · Physical Chemistry · Concept The short answer: A polymer sample contains chains of many lengths, so its molar mass is an average. Colligative methods count particles and give the number average; light scattering weights by mass and gives the weight average; viscosity gives a third value between them. Their ratio measures how broad the distribution is. Why there is…

ESR Spectroscopy: Detecting and Identifying Unpaired Electrons

September 16, 2026

Physical Chemistry · Spectroscopy ESR Spectroscopy: Detecting and Identifying Unpaired Electrons A technique that sees only species with unpaired electrons, which makes it uniquely selective for radicals and certain metal complexes. BSc & MSc · Spectroscopy · Concept The short answer: An unpaired electron in a magnetic field has two spin states, and transitions between them are observed in the microwave region. The g value locates the signal and identifies the environment; hyperfine splitting by nearby magnetic nuclei reveals where the unpaired electron is delocalised. The basic phenomenon An electron has spin, and in a magnetic field its two spin…

Silicates and Silicones: Structure From One Building Block

September 15, 2026

Inorganic Chemistry · Main Group Silicates and Silicones: Structure From One Building Block Every silicate is built from the same tetrahedron. What varies is how many corners are shared, and that single number determines the structure. BSc & MSc · Inorganic Chemistry · Concept The short answer: A silicate tetrahedron shares between zero and four of its corner oxygens with neighbours. Sharing none gives discrete anions, two gives chains or rings, three gives sheets, and four gives a three-dimensional network. Silicones are synthetic polymers with a silicon–oxygen backbone and organic side groups. The building block Every silicate contains silicon at…

The Thermodynamics of Mixing

September 14, 2026

Physical Chemistry · Thermodynamics The Thermodynamics of Mixing Why two liquids mix even when nothing energetic is gained, and what has to be true for them not to. BSc & MSc · Physical Chemistry · Concept The short answer: For an ideal solution the enthalpy of mixing is zero, so mixing is driven entirely by the entropy increase from having more accessible arrangements. Since that entropy term is always positive, ideal liquids always mix. Immiscibility therefore requires a positive enthalpy of mixing large enough to overcome it. The entropy of mixing Mixing increases the number of ways the molecules can…

Catalytic Cycles: Hydroformylation and the Wacker Process

September 14, 2026

Inorganic Chemistry · Catalysis Catalytic Cycles: Hydroformylation and the Wacker Process Industrial catalysis assembled from four elementary steps that repeat in different orders. Learn the steps and any cycle becomes readable. BSc & MSc · Inorganic Chemistry · Concept The short answer: Homogeneous catalytic cycles are built from a small set of elementary organometallic steps: oxidative addition, migratory insertion, reductive elimination and ligand substitution. Hydroformylation and the Wacker process are the two standard examples, and each is examined by asking which step does what. The elementary steps Step What changes Oxidation state Electron count Oxidative addition A bond adds across…

Crystal Defects and Non-Stoichiometry

September 13, 2026

Inorganic Chemistry · Solid State Crystal Defects and Non-Stoichiometry A perfect crystal would have zero entropy of disorder, which thermodynamics forbids above absolute zero. Defects are not flaws but a requirement. BSc & MSc · Inorganic Chemistry · Concept The short answer: Point defects exist in every real crystal because they increase entropy enough to lower the free energy despite costing enthalpy. Schottky defects remove ion pairs and reduce density; Frenkel defects relocate an ion and leave density unchanged. Non-stoichiometric compounds arise when defects are accompanied by a change in oxidation state. Why defects must exist Defects are thermodynamically required,…

Osmotic Pressure and the van’t Hoff Factor

September 13, 2026

Physical Chemistry · Solutions Osmotic Pressure and the van’t Hoff Factor The most sensitive of the colligative properties, and the only one practical for measuring the molar mass of very large molecules. BSc & MSc · Physical Chemistry · Concept The short answer: Osmotic pressure is the pressure that must be applied to stop solvent flowing through a semipermeable membrane into a solution. It is far larger than the other colligative effects at the same concentration, which is why it is the method of choice for polymers and proteins. The van’t Hoff factor corrects for dissociation or association of the…

Noble Gas Compounds: Why Xenon Reacts and Helium Does Not

September 12, 2026

Inorganic Chemistry · Main Group Noble Gas Compounds: Why Xenon Reacts and Helium Does Not The elements once believed inert form a well-defined set of compounds, and which ones form is entirely predictable from ionisation energy. BSc & MSc · Inorganic Chemistry · Concept The short answer: Xenon has a low enough ionisation energy to be oxidised by fluorine and oxygen. Its fluorides have structures predicted correctly by VSEPR once the lone pairs are counted, and the fluorides hydrolyse to oxides and oxofluorides. Helium and neon do not react, because their ionisation energies are far too high. Why xenon and…

Ionic Conductance, Kohlrausch’s Law and Transport Numbers

September 12, 2026