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 Electrochemical Cell in Chemistry An electrochemical cell is a device that converts chemical energy into electrical energy, or electrical energy into chemical energy, through redox (oxidation-reduction) reactions. --- Types of Electrochemical Cells There are two main types: 1. Galvanic Cell (Voltaic Cell) Converts chemical energy to electrical energy. Spontaneous redox reaction occurs. Used in batteries. Example: Daniel Cell (Zinc-Copper cell) 2. Electrolytic Cell Converts electrical energy to chemical energy. Non-spontaneous redox reaction occurs by applying external electricity. Used in electroplating, electrolysis of water. --- Basic Parts of an Electrochemical Cell 1. Electrodes: Anode: Oxidation occurs here. Cathode: Reduction occurs here. 2. Electrolyte: Solution that conducts electricity by movement of ions. 3. Salt Bridge (in Galvanic cells): Maintains electrical neutrality by allowing ion flow between two half-cells. 4. External Circuit: Electrons flow from anode to catho...

Overlapping (in Chemistry) Overlapping refers to the partial merging or sharing of atomic orbitals from two atoms to form a chemical bond , especially a covalent bond . 🔹 Definition: Overlapping is the partial merging of atomic orbitals of two atoms during the formation of a molecule, which allows electrons to be shared between them. 🔹 Types of Overlapping: s–s Overlapping: Between two s-orbitals . Example: H–H bond in H₂ molecule. s–p Overlapping: Between s-orbital of one atom and p-orbital of another. Example: H–Cl bond in HCl molecule. p–p Overlapping: Between two p-orbitals . Example: F–F bond in F₂ molecule. 🔹 Example: Hydrogen Molecule (H₂) Each hydrogen atom has 1s¹ configuration. When two hydrogen atoms approach each other, their 1s orbitals overlap . This overlap allows each atom to share one electron , forming a single covalent bond (σ bond). Diagram (simplified): H (1s) + H (1s) → H—H 🔹 Types of Bonds from Overlapping: ...

  ⚛️ Electron Gain Enthalpy (Δ eg H) Electron gain enthalpy is the amount of energy released or absorbed when an electron is added to an isolated gaseous atom to form a negative ion . 🔬 Definition: "Electron gain enthalpy is the enthalpy change when one mole of electrons is added to one mole of isolated gaseous atoms." 📘 General Reaction: X_{(g)} + e^- \rightarrow X^-_{(g)} \quad \Delta_{eg}H = isolated gaseous atom = anion formed = added electron = electron gain enthalpy 🔥 Key Points: Negative electron gain enthalpy : Energy is released (exothermic). Most nonmetals show this behavior. Example: Chlorine Cl_{(g)} + e^- \rightarrow Cl^-_{(g)} \quad \Delta_{eg}H = -349 \text{ kJ/mol} Positive electron gain enthalpy : Energy is absorbed (endothermic). Some elements (like noble gases or N) show this. Example: Nitrogen , Neon 📊 Trends in Periodic Table: Across a Period (→) : Electron gain enthalpy becomes more negative (more energy...

  💨 Isolated Gaseous Atom – Meaning: An isolated gaseous atom means: 👉 A single atom of an element 👉 In the gaseous state (not bonded to any other atom or molecule) 👉 That is completely free from external forces (like other atoms or molecules nearby) 🧪 In Simple Words: An isolated gaseous atom is a lone atom in the gas phase, existing independently , just like: A single He atom (Helium) floating alone in space Not forming a molecule like O₂ or H₂ Not in solid or liquid form 🔍 Why Important in Chemistry? It is a reference state used in: Ionization energy Electron affinity Enthalpy calculations Bond dissociation energies These properties are usually measured for an isolated gaseous atom because: There's no interference from other atoms. It gives the purest form of an element's energy or behavior. 🧠 Example: If we say: "The ionization energy of an isolated gaseous hydrogen atom is 1312 kJ/mol" It means: the energy required...

  Modern Periodic Law is one of the most important concepts in chemistry that explains the arrangement of elements in the modern periodic table. 🔬 Modern Periodic Law: "The physical and chemical properties of the elements are a periodic function of their atomic numbers." 📘 Explanation: This means that if the elements are arranged in the order of increasing atomic number , their properties repeat at regular intervals . It was proposed by Henry Moseley in 1913 , based on his experiments with X-rays. The atomic number (Z) is the number of protons in the nucleus of an atom, and it determines the identity and properties of the element. 🧪 Significance of Modern Periodic Law: Solved problems with Mendeleev’s periodic table, where elements were arranged by atomic mass . Helped correctly place elements like Argon (18) before Potassium (19) , even though Argon has more mass. Justified the existence of isotopes as they have the same atomic number but different mass...

 बफर विलयन (Buffer Solution) क्या है? – रसायन विज्ञान में परिभाषा: बफर विलयन एक ऐसा विलयन होता है जो अपने pH मान में अत्यधिक परिवर्तन नहीं होने देता, जब उसमें थोड़ी मात्रा में अम्ल (Acid) या क्षार (Base) मिलाया जाए। --- ✅ बफर विलयन के प्रकार: 1. अम्लीय बफर (Acidic Buffer): इसमें एक कमज़ोर अम्ल और उसके लवण (जो किसी मजबूत क्षार से बना हो) का मिश्रण होता है। उदाहरण: एसीटिक अम्ल (CH₃COOH) + सोडियम एसीटेट (CH₃COONa) 2. क्षारीय बफर (Basic Buffer): इसमें एक कमज़ोर क्षार और उसके लवण (जो किसी मजबूत अम्ल से बना हो) का मिश्रण होता है। उदाहरण: अमोनियम हाइड्रॉक्साइड (NH₄OH) + अमोनियम क्लोराइड (NH₄Cl) --- ⚙️ यह कैसे काम करता है? जब बफर विलयन में थोड़ा अम्ल डाला जाता है, तो यह अतिरिक्त H⁺ आयनों को न्यूट्रल कर देता है। जब थोड़ा क्षार (OH⁻ आयन) डाला जाता है, तो यह उसे भी न्यूट्रल कर देता है। इस प्रकार, pH मान लगभग स्थिर रहता है। --- 🧪 बफर विलयन का उपयोग: मानव शरीर में (जैसे – रक्त का pH लगभग 7.4 होता है, जो बफर के कारण स्थिर रहता है) रासायनिक प्रयोगों में, जहाँ एक निश्चित pH बनाए रखना आवश्यक होता ...