ABHYAS · CLASS 11–12 STUDENTS (CBSE AND STATE BOARDS), AND JEE/NEET ASPIRANTS REVISING THE BASICS

Class 11–12 Chemistry कक्षा 11–12 रसायन विज्ञान

Physical-chemistry numericals worked step by step: the mole concept, solution concentrations, empirical formulae, limiting reagents, gas laws, bond enthalpies, Kc, pH, cell potentials, kinetics and colligative properties, plus IUPAC naming and hybridisation.

Some basic concepts of chemistry

Mole concept: mass, moles and particlesMoles n = mass ÷ molar mass. Number of particles = n × Nₐ, where Nₐ = 6.022 × 10²³ mol⁻¹.
Empirical and molecular formula from % compositionAssume 100 g, convert each % to moles (÷ atomic mass), divide by the smallest, and round to whole numbers. Molecular formula = (empirical formula) × n, where n = molar mass ÷ empirical formula mass.
Stoichiometry and the limiting reagentDivide the moles of each reactant by its coefficient in the balanced equation. The smallest value marks the limiting reagent, and it decides how much product forms.

Solutions

States of matter

Ideal gas equation pV = nRTpV = nRT with p in atm, V in L, T in kelvin and R = 0.0821 L atm mol⁻¹ K⁻¹. Always convert °C to K first (T = t + 273).

Thermodynamics

Reaction enthalpy from bond enthalpiesΔH = Σ(bond enthalpies of bonds broken in reactants) − Σ(bond enthalpies of bonds formed in products). Breaking bonds needs energy; forming bonds releases it.

Equilibrium

Electrochemistry

Standard cell potential and ΔG°E°cell = E°cathode − E°anode (both as standard reduction potentials). The electrode with the higher E° is the cathode in a galvanic cell. ΔG° = −nFE°cell.

Chemical kinetics

Rate laws and first-order half-lifeFor a first-order reaction t½ = 0.693 ÷ k, independent of starting concentration. Find the order for a reactant by seeing how the rate changes when only its concentration changes.

Organic chemistry: basic principles

IUPAC names of simple organic compoundsPick the longest chain containing the functional group, number it to give the functional group (then substituents) the lowest locants, and add prefixes and the suffix.

Chemical bonding and molecular structure

Hybridisation of a central atomSteric number = σ bonds + lone pairs on the atom (a double or triple bond counts as one σ bond). 2 → sp, 3 → sp², 4 → sp³, 5 → sp³d, 6 → sp³d², 7 → sp³d³.