Fundamentals of Chemistry. Complete questions and answers.

What is the fundamental difference between matter and energy? ️ Matter has mass and occupies space, while energy is the capacity to do work or produce change without having mass or volume. How does atomic radius change across a period and why? ️ It decreases across a period due to increasing nuclear charge pulling electrons closer. What determines the reactivity of an element? ️ The number of valence electrons and how easily they are gained or lost. Why do noble gases rarely form compounds? ️ They have a complete valence shell, making them chemically stable. What is the role of orbitals in electron configuration? ️ Orbitals describe the probability region where an electron is likely to be found. How does electronegativity influence bond formation? ️ It determines how strongly atoms attract shared electrons in a bond. What is the difference between empirical and molecular formulas? ️ Empirical shows the simplest ratio, while molecular shows the actual number of atoms. Why is Avogadro’s number important in chemistry? ️ It links the microscopic world of atoms to measurable quantities in moles. What happens to particles during diffusion? ️ They move from regions of high concentration to low concentration due to kinetic energy. Why do solids have fixed shapes? ️ Their particles are closely packed and only vibrate in fixed positions. What is the significance of activation energy? ️ It is the minimum energy required for a reaction to occur. How does temperature affect reaction rate? ️ Higher temperature increases particle collisions and speeds up reactions. What is the difference between endothermic and exothermic reactions? ️ Endothermic absorbs heat, while exothermic releases heat. 2 What causes chemical equilibrium? ️ Equal rates of forward and reverse reactions. Why are catalysts important in reactions? ️ They lower activation energy and speed up reactions without being consumed. What is the pH scale used for? ️ To measure acidity or alkalinity of a solution. How do acids behave in water? ️ They donate hydrogen ions (H+). What defines a base in chemistry? ️ A substance that accepts hydrogen ions or produces OH− ions. Why is water considered a universal solvent? ️ It dissolves many substances due to its polarity. What is the difference between ionic and covalent bonds? ️ Ionic involves electron transfer, covalent involves electron sharing. How does pressure affect gases? ️ Increasing pressure decreases volume if temperature is constant. What is Boyle’s Law? ️ It states pressure is inversely proportional to volume at constant temperature. What happens during oxidation? ️ Loss of electrons. What happens during reduction? ️ Gain of electrons. Why are oxidation and reduction always paired? ️ Because electrons lost by one substance are gained by another. What is the role of valence electrons? ️ They determine how an element bonds with others. Why do metals conduct electricity? ️ They have free-moving electrons. What is a mole in chemistry? ️ A unit representing 6.022 × 1023 particles. 3 How is density calculated? ️ Mass divided by volume. Why does ice float on water? ️ It is less dense due to hydrogen bonding structure. What is a solution? ️ A homogeneous mixture of solute and solvent. What determines solubility? ️ Temperature, pressure, and nature of substances. What is the difference between saturated and unsaturated solutions? ️ Saturated holds maximum solute, unsaturated can dissolve more. What is a precipitate? ️ An insoluble solid formed in a reaction. Why do reactions occur faster in powdered solids? ️ Increased surface area leads to more collisions. What is the law of conservation of mass? ️ Mass is neither created nor destroyed in a reaction. How does concentration affect reaction rate? ️ Higher concentration increases collision frequency. What is a buffer solution? ️ A solution that resists pH changes. Why is carbon unique in chemistry? ️ It can form four bonds and long chains. What is isomerism? ️ Compounds with same formula but different structures. What is the difference between alkanes and alkenes? ️ Alkanes have single bonds, alkenes have double bonds. What is hybridization? ️ Mixing of atomic orbitals to form new orbitals. What determines molecular shape? ️ Electron pair repulsion around the central atom.