Chemistry NCERT & Official PYQ Mapped

Chemistry Formulas & Periodic Reference

A clear, structured Chemistry reference handbook for board examinations and competitive entrance tests. Covers Physical Chemistry numerical formulas, stoichiometry, and fundamental inorganic/organic reaction summaries.

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1. Mole Concept & Stoichiometry

The foundation of chemical quantitative calculations.

Number of Moles (n)

n = Mass (g) / Molar Mass (g/mol) = N / N_A = Volume at STP (L) / 22.4 L

Variables & Units: N = Number of particles, N_A = Avogadro’s Constant (6.022 × 10²³ particles/mol)

Exam Application: At STP (0°C, 1 atm), 1 mole of any ideal gas occupies 22.4 liters.

Molarity (M)

Molarity (M) = [Moles of Solute] / [Volume of Solution in Liters]

Variables & Units: Unit = mol/L or Molar (M)

Exam Application: Dilution Equation: M₁V₁ = M₂V₂ (Temperature-dependent concentration unit).

Molality (m)

Molality (m) = [Moles of Solute] / [Mass of Solvent in kg]

Variables & Units: Unit = mol/kg or molal (m)

Exam Application: Molality does NOT change with temperature because mass is independent of temperature.

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2. Gas Laws & Chemical Thermodynamics

Behavior of gases and thermal state functions in chemical reactions.

Ideal Gas Equation

P · V = n · R · T

Variables & Units: P = Pressure (atm/Pa), V = Volume (L/m³), n = Moles, R = Universal gas constant (0.0821 L·atm/mol·K or 8.314 J/mol·K), T = Temperature (Kelvin, K = °C + 273.15)

Exam Application: Combines Boyle’s Law (P ∝ 1/V), Charles’s Law (V ∝ T), and Avogadro’s Law (V ∝ n).

First Law of Thermodynamics

ΔU = q + w (IUPAC convention)

Variables & Units: ΔU = Change in internal energy, q = Heat absorbed by system, w = Work done on system (w = -P_ext · ΔV for expansion)

Exam Application: In an isolated system, energy is conserved.

3. Periodic Table Trends

Summary of how atomic and chemical properties vary across periods and groups.

Atomic Radius Trend

Across Period (Left to Right): DecreasesDown Group (Top to Bottom): Increases

Variables & Units: Effective nuclear charge increases across a period pulling electron clouds closer.

Exam Application: Cation is always smaller than its parent atom; Anion is always larger.

Ionization Energy & Electronegativity

Across Period: IncreasesDown Group: Decreases

Variables & Units: Fluorine (F) is the most electronegative element (Pauling scale: 4.0).

Exam Application: Noble gases have extraordinarily high ionization enthalpy due to stable full octets.