CBSE · Class 11
Chemistry Formulas for Class 11
Chapter-wise formula tables for CBSE Class 11 Chemistry 2026-27 — Mole Concept, Thermodynamics, Equilibrium, Atomic Structure and more.
For reference only. Always verify formulas and information against your official NCERT textbooks or board-prescribed materials before use in exams. Learnizo does not guarantee absolute accuracy.
Ch 1.Some Basic Concepts of Chemistry (Mole Concept)
| Formula / Relation | Expression |
|---|---|
| Molar Mass | M = mass (g) / moles (n) |
| Number of Moles | n = given mass / molar mass = N / Nₐ |
| Molarity | M = moles of solute / volume of solution (L) |
| Mole Fraction | χ_A = n_A / (n_A + n_B) |
| Mass % (w/w) | w% = (mass of component / total mass) × 100 |
| ppm | ppm = (mass of component / total mass) × 10⁶ |
| Empirical to Molecular Formula | Mol. formula = n × empirical formula; n = M / empirical mass |
| % Yield | % yield = (actual yield / theoretical yield) × 100 |
Ch 2.Atomic Structure
| Formula / Relation | Expression |
|---|---|
| Bohr Radius (nth orbit) | rₙ = 0.529 × n² / Z Å |
| Energy of nth Orbit (H-like) | Eₙ = −13.6 × Z² / n² eV |
| Frequency of Photon (Bohr) | ΔE = hν = hc/λ |
| de Broglie Wavelength | λ = h / mv = h / p |
| Heisenberg Uncertainty Principle | Δx · Δp ≥ h / 4π |
| Rydberg Equation | 1/λ = R_H(1/n₁² − 1/n₂²) |
| Velocity of nth Orbit (Bohr) | vₙ = 2.18 × 10⁶ × Z / n m/s |
| Max electrons in subshell | 2(2l + 1) |
Ch 3.Chemical Bonding and Molecular Structure
| Formula / Relation | Expression |
|---|---|
| Formal Charge | FC = V − N − B/2 |
| Bond Order (MO Theory) | BO = (bonding e⁻ − antibonding e⁻) / 2 |
| Dipole Moment | μ = q × d |
| VSEPR: Steric Number | SN = bonding pairs + lone pairs on central atom |
Ch 4.States of Matter (Gases)
| Formula / Relation | Expression |
|---|---|
| Boyle's Law | P₁V₁ = P₂V₂ (constant T, n) |
| Charles's Law | V₁/T₁ = V₂/T₂ (constant P, n) |
| Gay-Lussac's Law | P₁/T₁ = P₂/T₂ (constant V, n) |
| Ideal Gas Law | PV = nRT |
| Dalton's Law | P_total = P_A + P_B + P_C + … |
| Graham's Law of Diffusion | r₁/r₂ = √(M₂/M₁) |
| van der Waals Equation | (P + an²/V²)(V − nb) = nRT |
| Root Mean Square Speed | u_rms = √(3RT/M) |
| Average Speed | u_avg = √(8RT/πM) |
| Most Probable Speed | u_mp = √(2RT/M) |
| Compressibility Factor | Z = PV/nRT |
Ch 5.Thermodynamics
| Formula / Relation | Expression |
|---|---|
| First Law | ΔU = q + w |
| Enthalpy | H = U + PV; ΔH = ΔU + ΔnᵍRT |
| Hess's Law | ΔH_reaction = ΣΔH_f(products) − ΣΔH_f(reactants) |
| Entropy Change | ΔS = q_rev / T |
| Gibbs Free Energy | ΔG = ΔH − TΔS |
| Standard Gibbs Energy & K | ΔG° = −RT ln K |
| Bond Enthalpy Approach | ΔH_rxn = ΣBE(bonds broken) − ΣBE(bonds formed) |
| Cp − Cv (ideal gas) | Cp − Cv = R |
Ch 6.Chemical Equilibrium
| Formula / Relation | Expression |
|---|---|
| Equilibrium Constant (Kc) | Kc = [C]^c[D]^d / [A]^a[B]^b |
| Kp from Kc | Kp = Kc(RT)^Δnᵍ |
| Reaction Quotient (Q) | Same expression as Kc, but with any concentrations |
| Degree of Dissociation (α) | α = (moles dissociated / initial moles) |
| Le Chatelier: Temperature Effect | Increasing T shifts equilibrium in endothermic direction |
Ch 7.Ionic Equilibrium
| Formula / Relation | Expression |
|---|---|
| pH | pH = −log[H⁺] |
| Kw | Kw = [H⁺][OH⁻] = 1 × 10⁻¹⁴ at 25°C |
| Ka (weak acid) | Ka = [H⁺][A⁻] / [HA] |
| pH of weak acid | pH = ½(pKa − log C) |
| Henderson-Hasselbalch (buffer) | pH = pKa + log([A⁻]/[HA]) |
| Solubility Product (Ksp) | Ksp = [M^m⁺]^m[X^n⁻]^n for M_mX_n |
| Molar Solubility from Ksp | For MX: s = √Ksp; for MX₂: s = (Ksp/4)^(1/3) |
Ch 8.Redox Reactions
| Formula / Relation | Expression |
|---|---|
| Oxidation Number Rules | Sum of ON in neutral molecule = 0; in ion = charge |
| Balancing by Half-Reaction (acidic) | Balance O with H₂O, H with H⁺, then charge with e⁻ |
| n-factor (acid-base) | n = H⁺ or OH⁻ exchanged per molecule |
| n-factor (redox) | n = change in oxidation state × number of atoms changing |
Frequently Asked Questions
Which is the most important chapter for formulas in Class 11 Chemistry?
Thermodynamics, States of Matter (Gases), and Ionic Equilibrium are the most formula-heavy chapters in Class 11 Chemistry. Mole Concept is the foundation — get that right first. Thermodynamics and Equilibrium together carry roughly 30% of the board exam marks.
What is the ideal gas equation and when is it used?
The ideal gas equation is PV = nRT, where P = pressure (atm), V = volume (L), n = moles, R = 0.0821 L·atm·mol⁻¹·K⁻¹ (or 8.314 J·mol⁻¹·K⁻¹), and T = temperature in Kelvin. It is used to calculate any one gas property given the others for gases at normal conditions.
How do I remember the de Broglie wavelength formula?
λ = h/mv = h/p. Think of it as 'Planck's constant divided by momentum.' Since h = 6.626 × 10⁻³⁴ J·s is tiny, the wavelength is only significant for very light or very slow particles. For electrons it is measurable; for a cricket ball it is negligibly small.
What is the Henderson-Hasselbalch equation used for?
The Henderson-Hasselbalch equation (pH = pKa + log([A⁻]/[HA])) calculates the pH of a buffer solution. When [A⁻] = [HA], pH = pKa. Buffer capacity is maximum at pH = pKa. This appears in 3-mark numericals in CBSE boards.
What is the difference between Kc and Kp?
Kc uses molar concentrations (mol/L) and Kp uses partial pressures (atm). They are related by Kp = Kc(RT)^Δnᵍ. When Δnᵍ = 0 (no change in moles of gas), Kp = Kc. For reactions involving only solids and liquids, Kp = Kc = 1.
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