CBSE Class 11 Chemistry Formulas and Equations Chapter Wise 2027 — Complete List | Padhaao Blog

In short: Class 11 Chemistry is the foundation year — every formula you learn here carries into Class 12, competitive exams like JEE and NEET, and even college chemistry. This post covers every important formula and equation organized by NCERT chapter: from mole concept to hydrocarbons. Physical Chemistry chapters (1–7) are formula-heavy; Organic and Inorganic chapters rely more on reactions and trends. Bookmark this for daily 15-minute revision sessions.

Chapter 1: Some Basic Concepts of Chemistry

Formula	Expression	Use
Mole concept	1 mole = 6.022 × 10²³ particles (Avogadro's number, Nₐ)	Converting between particles and moles
Molar mass	M = mass of 1 mole of substance (g/mol)	Relating mass to moles
Number of moles	n = given mass / molar mass = W/M	Core calculation
Number of particles	N = n × Nₐ = (W/M) × 6.022 × 10²³	Finding atoms/molecules from mass
Molarity	M = moles of solute / volume of solution in litres	Solution concentration
Molality	m = moles of solute / mass of solvent in kg	Temperature-independent concentration
Mole fraction	xₐ = nₐ/(nₐ + n_b)	Composition of mixtures
Mass percentage	(mass of solute / mass of solution) × 100	Percentage concentration
Empirical formula	Simplest whole-number ratio of atoms	From percentage composition
Molecular formula	n × empirical formula (n = molecular mass / empirical formula mass)	Actual formula of compound
Limiting reagent	Reagent that produces the least amount of product	Stoichiometry problems
Percentage yield	(actual yield / theoretical yield) × 100	Efficiency of reaction

Mole concept is tested in every exam. For a broader study approach, see how to study chemistry: organic, inorganic, physical.

Chapter 2: Structure of Atom

Formula	Expression	Notes
Atomic number	Z = number of protons	Defines the element
Mass number	A = protons + neutrons	Isotopes differ in A
Wavelength-frequency	c = νλ	c = 3 × 10⁸ m/s
Energy of photon	E = hν = hc/λ	h = 6.626 × 10⁻³⁴ J·s
Photoelectric effect	hν = φ + ½mv²	φ = work function
De Broglie wavelength	λ = h/mv = h/p	Wave-particle duality
Heisenberg uncertainty	Δx × Δp ≥ h/4π	Cannot know both x and p precisely
Bohr's radius	rₙ = 0.529 × n²/Z Å	Hydrogen-like atoms
Bohr's energy	Eₙ = −13.6 × Z²/n² eV	Negative = bound state
Bohr's velocity	vₙ = 2.18 × 10⁶ × Z/n m/s	Speed of electron
Wave number	ν̄ = 1/λ = Rₕ[1/n₁² − 1/n₂²]	Rₕ = 1.097 × 10⁷ m⁻¹
Quantum numbers	n (principal), l (azimuthal, 0 to n−1), mₗ (magnetic, −l to +l), mₛ (spin, ±½)	Electron address
Max electrons in shell	2n²	n=1→2, n=2→8, n=3→18
Max electrons in subshell	2(2l+1)	s→2, p→6, d→10, f→14

Chapter 3: Classification of Elements and Periodicity in Properties

This chapter is trend-based rather than formula-based. Key quantitative relationships:

Property	Trend Along Period (→)	Trend Down Group (↓)
Atomic radius	Decreases	Increases
Ionization enthalpy	Increases	Decreases
Electron gain enthalpy	Becomes more negative (generally)	Becomes less negative
Electronegativity	Increases	Decreases
Metallic character	Decreases	Increases
Non-metallic character	Increases	Decreases

Key formulas:

IE₁ < IE₂ < IE₃ (successive ionization enthalpies increase)
Electronegativity (Pauling scale): difference determines bond polarity

Chapter 4: Chemical Bonding and Molecular Structure

Concept	Formula / Rule	Notes
Formal charge	FC = valence electrons − non-bonding electrons − ½(bonding electrons)	Determines best Lewis structure
Bond order	BO = (bonding electrons − antibonding electrons)/2	Higher BO = stronger bond
Dipole moment	μ = q × d (charge × distance)	Unit: Debye (D)
% ionic character	(observed μ / calculated μ for 100% ionic) × 100	Fajan's rules
Hybridization	½[V + M − C + A]	V=valence electrons, M=monovalent atoms, C=cation charge, A=anion charge
sp hybridization	2 electron pairs → linear (180°)	BeCl₂, C₂H₂
sp² hybridization	3 electron pairs → trigonal planar (120°)	BF₃, C₂H₄
sp³ hybridization	4 electron pairs → tetrahedral (109.5°)	CH₄, NH₃ (107°), H₂O (104.5°)

Chapter 5: States of Matter

Gas Laws

Law	Formula	Condition
Boyle's Law	P₁V₁ = P₂V₂	Constant T and n
Charles's Law	V₁/T₁ = V₂/T₂	Constant P and n
Gay-Lussac's Law	P₁/T₁ = P₂/T₂	Constant V and n
Avogadro's Law	V ∝ n	Constant T and P
Ideal Gas Equation	PV = nRT	R = 8.314 J/(mol·K) = 0.0821 L·atm/(mol·K)
Combined Gas Law	P₁V₁/T₁ = P₂V₂/T₂	Constant n
Dalton's Law	P_total = p₁ + p₂ + p₃ + ...	Partial pressures
Partial pressure	pᵢ = xᵢ × P_total	xᵢ = mole fraction
Graham's Law	r₁/r₂ = √(M₂/M₁)	Rate of diffusion
Kinetic energy	KE = (3/2)kT per molecule = (3/2)RT per mole	k = R/Nₐ
Root mean square speed	u_rms = √(3RT/M)	M in kg/mol
Average speed	u_avg = √(8RT/πM)
Most probable speed	u_mp = √(2RT/M)	u_mp < u_avg < u_rms
Van der Waals equation	(P + an²/V²)(V − nb) = nRT	a = intermolecular forces, b = volume correction
Compressibility factor	Z = PV/nRT	Z = 1 for ideal gas

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Chapter 6: Thermodynamics

Formula	Expression	Notes
First Law	ΔU = q + w	q = heat, w = work
Work (expansion)	w = −P_ext × ΔV (irreversible); w = −nRT ln(V₂/V₁) (reversible isothermal)	Negative w = work done BY system
Enthalpy	H = U + PV; ΔH = ΔU + ΔnₘRT	Δnₘ = moles of gaseous products − reactants
Heat capacity	q = nCΔT; Cp − Cv = R	Cp = constant pressure, Cv = constant volume
Hess's Law	ΔH_reaction = Σ ΔH_f(products) − Σ ΔH_f(reactants)	Enthalpy is a state function
Bond enthalpy	ΔH = Σ bond enthalpies (reactants) − Σ bond enthalpies (products)	Breaking bonds is endothermic
Lattice enthalpy	Born-Haber cycle	Relates lattice energy to measurable quantities
Entropy	ΔS = q_rev/T	Measure of disorder
Gibbs free energy	ΔG = ΔH − TΔS	ΔG < 0 → spontaneous
Gibbs criteria	ΔG < 0 → spontaneous; ΔG = 0 → equilibrium; ΔG > 0 → non-spontaneous
Equilibrium temperature	T = ΔH/ΔS (when ΔG = 0)	At this T, reaction is at equilibrium

Chapter 7: Equilibrium

Chemical Equilibrium

Formula	Expression	Notes
Equilibrium constant (Kc)	Kc = [products]ⁿ/[reactants]ᵐ	Concentrations at equilibrium
Equilibrium constant (Kp)	Kp = (partial pressures of products)/(partial pressures of reactants)	For gaseous reactions
Relation Kp and Kc	Kp = Kc(RT)^Δn	Δn = gaseous product moles − gaseous reactant moles
Reaction quotient	Q = same form as K but with any concentrations	Q < K → forward; Q > K → backward
ΔG° and K	ΔG° = −RT ln K	Links thermodynamics to equilibrium
Le Chatelier's Principle	System shifts to oppose the change	Qualitative — no formula

Ionic Equilibrium

Formula	Expression
Degree of dissociation	α = dissociated amount / initial amount
Ostwald dilution law	Ka = Cα² / (1−α) ≈ Cα² (for weak electrolyte)
pH	pH = −log[H⁺]
pOH	pOH = −log[OH⁻]
Relation	pH + pOH = 14 (at 25°C)
Ionic product of water	Kw = [H⁺][OH⁻] = 10⁻¹⁴ at 25°C
Henderson-Hasselbalch	pH = pKa + log([salt]/[acid]); pOH = pKb + log([salt]/[base])
Buffer capacity	Ratio [salt]/[acid] determines buffering range
Solubility product	Ksp = [cation]ᵐ[anion]ⁿ (for MₘAₙ)
Common ion effect	Addition of common ion suppresses dissociation

Chapter 8: Redox Reactions

Concept	Formula / Rule
Oxidation number rules	Free element = 0; monoatomic ion = charge; H = +1 (except metal hydrides = −1); O = −2 (except peroxides = −1, OF₂ = +2)
Balancing by oxidation number	Identify oxidation and reduction half-reactions; balance electrons transferred
Balancing by half-reaction (ion-electron)	Balance atoms, then charge using e⁻, then combine
n-factor (equivalent concept)	For acid: basicity; for base: acidity; for redox: electrons transferred per molecule

Chapter 9: Hydrogen

Key reactions (not formula-heavy):

Electrolysis of water: 2H₂O → 2H₂ + O₂
H₂ + Cl₂ → 2HCl (in presence of light)
Water hardness: Ca(HCO₃)₂ → CaCO₃ + H₂O + CO₂ (temporary, on boiling)

Chapters 10–11: s-Block and p-Block Elements

These chapters focus on reactions and trends, not formulas. Key quantitative:

Property	Formula
Diagonal relationship	Li ~ Mg, Be ~ Al, B ~ Si
Solubility trend (s-block hydroxides)	Increases down the group
Solubility trend (s-block carbonates)	Decreases down the group (Group 2)
Thermal stability of carbonates	Increases down the group

Chapter 12: Organic Chemistry — Some Basic Principles

Concept	Formula / Rule
Degree of unsaturation (DBE)	DBE = (2C + 2 + N − H − X)/2
Homologous series	CₙH₂ₙ₊₂ (alkanes), CₙH₂ₙ (alkenes/cycloalkanes), CₙH₂ₙ₋₂ (alkynes)
IUPAC naming	Longest chain + substituent positions + functional group suffix
Inductive effect (+I, −I)	Through sigma bonds; decreases with distance
Electromeric effect (+E, −E)	Temporary shift of π electrons under influence of attacking reagent
Hyperconjugation	No-bond resonance; stability: 3° > 2° > 1° carbocation

Chapter 13: Hydrocarbons

Reaction Type	General Equation	Conditions
Combustion (alkanes)	CₙH₂ₙ₊₂ + (3n+1)/2 O₂ → nCO₂ + (n+1)H₂O	Complete combustion
Halogenation (alkanes)	CH₄ + Cl₂ → CH₃Cl + HCl	UV light, free radical mechanism
Addition of H₂ to alkenes	CₙH₂ₙ + H₂ → CₙH₂ₙ₊₂	Ni/Pt/Pd catalyst
Addition of HBr (Markovnikov)	CH₃CH=CH₂ + HBr → CH₃CHBrCH₃	Ionic addition, H to C with more H
Anti-Markovnikov (Peroxide effect)	CH₃CH=CH₂ + HBr → CH₃CH₂CH₂Br	Peroxide (ROOR), only with HBr
Ozonolysis (alkenes)	R₁R₂C=CR₃R₄ → R₁R₂C=O + R₃R₄C=O	O₃ then Zn/H₂O
Addition to alkynes	HC≡CH + 2H₂ → CH₃CH₃	Ni catalyst
Lindlar's catalyst (partial)	HC≡CH + H₂ → CH₂=CH₂ (cis)	Pd/BaSO₄ with quinoline (poisoned)
Birch reduction	C₆H₆ + Na/liquid NH₃ + alcohol → 1,4-cyclohexadiene	Partial reduction of benzene

Quick Summary — Formula Count by Chapter

Chapter	Approx. Formulas	Priority
Some Basic Concepts	12	🔴 High
Atomic Structure	14	🔴 High
Chemical Bonding	8	🟡 Medium
States of Matter	15	🔴 High
Thermodynamics	12	🔴 High
Equilibrium	14	🔴 High
Redox	4	🟢 Low
s-Block & p-Block	Reactions only	🟡 Medium
Organic Principles	6	🟡 Medium
Hydrocarbons	Reactions	🟡 Medium

For strategic study ordering, see the how to study smart not hard guide.

Frequently Asked Questions

How many formulas are there in CBSE Class 11 Chemistry?

There are approximately 85–90 important formulas and equations across all chapters. The most formula-dense chapters are States of Matter (15), Atomic Structure (14), Equilibrium (14), Thermodynamics (12), and Some Basic Concepts (12). Organic Chemistry chapters have more reactions than formulas.

Should I memorize all formulas or understand the derivations?

For Class 11, understanding is more important than memorization because these formulas appear again in Class 12 and competitive exams. That said, you must be able to recall and apply them quickly. The best approach: understand once, then practice 10 numericals per formula to make recall automatic.

Which Class 11 Chemistry formulas are most important for JEE/NEET?

The ideal gas equation (PV = nRT), Gibbs free energy (ΔG = ΔH − TΔS), Kp-Kc relationship, Bohr model equations, and the mole concept formulas are tested heavily in both JEE and NEET. Every single formula from Thermodynamics and Equilibrium appears in entrance exams.

Is Class 11 Chemistry harder than Class 12?

The formula density is similar, but Class 11 introduces many concepts from scratch (mole concept, atomic orbitals, thermodynamic laws) whereas Class 12 builds on them. Students who struggle in Class 11 often find Class 12 easier because the foundation is set. Build that foundation strong using these formulas.

How do I revise all Class 11 Chemistry formulas before the exam?

Spend 15 minutes daily: Day 1 — Chapter 1–2, Day 2 — Chapter 3–4, Day 3 — Chapter 5–6, Day 4 — Chapter 7, Day 5 — Chapters 8–11, Day 6 — Chapters 12–13, Day 7 — full formula test from memory. Repeat this 7-day cycle until the exam.

Are there any differences between CBSE and JEE syllabus for Class 11 Chemistry?

The NCERT syllabus is the base for both. JEE goes deeper in certain topics — more complex equilibrium problems, advanced thermodynamics calculations, and additional organic reaction mechanisms. But every CBSE formula listed here is also relevant for JEE Main.

CBSE Class 11 Chemistry Formulas and Equations Chapter Wise 2027 — Complete List