Mole Relationships
n moles, m mass, Mᵣ molar mass, c concentration (mol dm⁻³), V volume (dm³).
n = m / Mᵣ n = cV (solution, V in dm³) n = volume (gas) / 24.0 dm³ at rtp Cambridge International A Level 9701
⚗️ International A Level Chemistry Formula Sheet 2025
Thermodynamics, kinetics, equilibria, organic calculations and analytical chemistry formulas curated for Cambridge 9701 papers.
Physical Chemistry Organic Chemistry Analytical Techniques
Keep Your Chemistry Calculations Consistent
From enthalpy changes to electrode potentials and titration steps, this sheet keeps the essential relationships at your fingertips. Combine them with careful units and stoichiometry to present precise, examiner-friendly answers.
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Thermodynamics and energetics equations
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Electrochemistry potentials and cell emf
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Titration & volumetric analysis reminders
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Organic yield and empirical calculations
Stoichiometry & Solutions
Ideal Gas Equation
p pressure, V volume, n moles, R gas constant (8.31 J mol⁻¹ K⁻¹), T temperature in kelvin. Use SI units throughout.
pV = nRT Percentage Yield & Purity
Actual yield measured experimentally; theoretical yield from balanced equation; purity compares mass of pure substance to total sample.
Percentage yield = (Actual yield / Theoretical yield) × 100% Percentage purity = (Mass of pure substance / Mass of impure sample) × 100% Empirical & Molecular Formula
Divide mass by atomic mass to obtain moles, simplify ratio for empirical formula. Molecular formula = (Mr of compound / Mr empirical) × empirical formula.
Thermodynamics & Energetics
Enthalpy Change Relationships
q heat absorbed, m mass, c specific heat capacity, ΔT temperature change, ΔH enthalpy change, n moles of limiting reagent. Use negative sign for exothermic reactions; mass is total solution or substance heated.
q = mcΔT ΔH = −q / n (per mole of limiting reagent) Hess’s Law
ΔH (overall) = Σ ΔH (steps). Construct cycles to calculate unknown enthalpy change.
Bond Enthalpy
Average bond enthalpies give approximate values; note state limitations.
ΔH = Σ (bond enthalpies broken) − Σ (bond enthalpies formed) Born-Haber Cycle
Remember lattice enthalpy sign conventions: formation is negative, dissociation positive.
ΔH_formation = Σ(ΔH_sub + IE + ½ BDE + EA + …) − U Entropy & Gibbs Free Energy
ΔS entropy change, ΔH enthalpy change, T temperature in kelvin, ΔG Gibbs free energy. ΔG < 0 indicates spontaneity; convert ΔS to J mol⁻¹ K⁻¹ if needed.
ΔS = Σ S_products − Σ S_reactants ΔG = ΔH − TΔS Chemical Equilibria & Kinetics
Equilibrium Constant (Kc)
Square brackets denote equilibrium concentrations in mol dm⁻³. Excludes pure solids/liquids.
Kc = [Products]^coefficients / [Reactants]^coefficients Reaction Quotient (Q)
Q has same form as Kc but uses initial or non-equilibrium values to predict shift. Equilibrium Partial Pressures (Kp)
P represents equilibrium partial pressure (Pa or atm). Consistent units cancel in ratio.
Kp = (P_products)^coefficients / (P_reactants)^coefficients Rate Equations
rate change in concentration per unit time, k rate constant, [A] and [B] reactant concentrations, m and n reaction orders. Initial rates method or half-life comparisons determine orders.
rate = k[A]^m[B]^n Units of k depend on overall order = m + n Arrhenius Equation
k rate constant, A frequency factor, Eₐ activation energy, R gas constant, T temperature (K). Linear form: ln k = ln A − (Eₐ/R)(1/T); slope = −Eₐ/R.
k = Ae^{−Eₐ/RT} Half-life (First Order)
t½ time for concentration to halve; k first-order rate constant. Constant half-life indicates first-order reaction.
t½ = ln 2 / k Acids, Bases & Buffer Systems
pH & Ion Product
[H⁺] hydrogen ion concentration, [OH⁻] hydroxide concentration, Kw ionic product of water.
pH = −log₁₀[H⁺] pOH = −log₁₀[OH⁻] Kw = [H⁺][OH⁻] = 1.00 × 10⁻¹⁴ mol² dm⁻⁶ at 25°C pH + pOH = 14 at 25°C Acid Dissociation Constant
For weak acids, [H⁺] ≈ [A⁻] and [HA] ≈ initial concentration.
Ka = [H⁺][A⁻] / [HA] pKa = −log₁₀ Ka Buffer Calculations
Valid when buffer components are in large excess compared to added acid/base.
pH = pKa + log₁₀([A⁻]/[HA]) Titration Stoichiometry
n_acid = n_base at equivalence. Use c₁V₁ = c₂V₂ for monoprotic systems; adjust for stoichiometric coefficients.
Electrochemistry & Redox
Standard Electrode Potentials
Combine half-equations with more positive E° as reduction at cathode.
E°cell = E°(reduced) − E°(oxidised) Gibbs Free Energy & Cell Potential
n = moles of electrons transferred; F = 96500 C mol⁻¹.
ΔG° = −nFE° Nernst Equation (qualitative syllabus awareness)
E = E° − (0.0592/n) log₁₀(Q) at 298 K. Demonstrate understanding of concentration effects.
Electrolysis Calculations
Q charge passed, I current, t time, n amount of substance, z electrons per ion, F Faraday constant (96500 C mol⁻¹).
Q = It n = Q / (zF) Organic & Analytical Calculations
Percentage Composition from Combustion
Convert CO₂ → C and H₂O → H moles, subtract from sample mass to obtain O or other elements.
nucleophilic substitution rate comparison
Rate ∝ concentration for SN1 (first order) vs SN2 (second order). Use kinetics data to justify mechanism.
IR & NMR Key Ranges
IR fingerprint: C=O ~1700 cm⁻¹, O-H broad 3200–3600 cm⁻¹. ¹H NMR splitting: n + 1 rule.
Chromatography
R_f = Distance travelled by component / Distance travelled by solvent front Partition coefficient (K_d)
K_d = Concentration in stationary phase / Concentration in mobile phase How to Use This Formula Sheet
Boost your Cambridge exam confidence with these proven study strategies from our tutoring experts.
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Show Complete Stoichiometry
Write balanced equations before calculating moles or enthalpy changes so you can check limiting reagents quickly.
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Quote Data Sources
When using tabulated data (E°, bond energies, lattice enthalpy), cite the data booklet to support your approach.
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Track Units Carefully
Convert cm³ to dm³, kJ to J and °C to K before substituting into thermodynamic or gas equations.
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Link Calculations to Trends
After each numeric answer, comment on what it implies about equilibrium position, spontaneity or mechanism to earn explanation marks.
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Formulas align with the Cambridge International AS & A Level Chemistry (9701) syllabus and data booklet tables.
Standard constants: F = 9.65×10⁴ C mol⁻¹, R = 8.31 J mol⁻¹ K⁻¹, Avogadro’s number = 6.02×10²³ mol⁻¹.