Question types
Every kind of calculation in UnoffIChO, from A-Level to IChO. Each page has a worked example, the method and the mistakes people usually make; then practise it in the app with new numbers every time.
Thermodynamics
- ΔG from ΔH and ΔSA-Level (AQA) · C3L6 · UKChO Round 1 · IChO
- K from ΔG°UKChO Round 1 · UKChO Round 2 · IChO
- ΔG° from KUKChO Round 1 · UKChO Round 2 · IChO
- K from ΔH° and ΔS°UKChO Round 1 · UKChO Round 2 · IChO
- van 't Hoff: K at a new temperatureUKChO Round 2 · IChO
- Moles of an ideal gasA-Level (AQA) · C3L6 · UKChO Round 1 · IChO
- ΔH at another temperature (Kirchhoff)UKChO Round 2 · IChO
- Boiling point at reduced pressureUKChO Round 2 · IChO
- Entropy change on heatingUKChO Round 2 · IChO
- Hess's law from enthalpies of formationA-Level (AQA) · C3L6 · UKChO Round 1 · IChO
- ΔH from a bomb-calorimeter ΔUUKChO Round 1 · UKChO Round 2 · IChO
- Enthalpy of combustion from a calorimetry experimentA-Level (AQA)
- Enthalpy of neutralisationA-Level (AQA)
- ΔfH from enthalpies of combustionA-Level (AQA)
- ΔH from mean bond enthalpiesA-Level (AQA)
- An unknown bond enthalpy from ΔHA-Level (AQA)
- Born–Haber cycle: lattice enthalpy of NaClA-Level (AQA)
- Born–Haber cycle: lattice enthalpy of MgCl₂A-Level (AQA)
- ΔS from standard entropiesA-Level (AQA)
- Temperature at which a reaction becomes feasibleA-Level (AQA)
- ΔG from enthalpies of formation and entropiesA-Level (AQA)
- Enthalpy of solution from a thermodynamic cycleUKChO Round 1
- Methanol synthesis: K from tabulated dataUKChO Round 1 · UKChO Round 2 · IChO
Kinetics
- First order: concentration after time tC3L6 · UKChO Round 1 · UKChO Round 2 · IChO
- Activation energy from two rate constantsA-Level (AQA) · C3L6 · UKChO Round 1 · IChO
- Second-order half-lifeUKChO Round 1 · UKChO Round 2 · IChO
- Steady state: A ⇌ I → PUKChO Round 2 · IChO
- Pre-equilibrium then half-lifeUKChO Round 2 · IChO
- Lindemann–Hinshelwood fall-offUKChO Round 2 · IChO
- Michaelis–Menten rateUKChO Round 2 · IChO
- Radioactive decay: elapsed timeC3L6 · UKChO Round 1 · IChO
- ΔG‡ from a rate constantIChO
- Time for a second-order reaction to reach a concentrationUKChO Round 1
- Rate constant from total pressureUKChO Round 1
- Apparent activation energy of a pre-equilibrium mechanismUKChO Round 2 · IChO
- 2NO + O₂: pre-equilibrium with bimolecular stepsUKChO Round 2 · IChO
- Lindemann mechanism at a given pressureUKChO Round 2 · IChO
- From ΔG‡ to a reaction time at another temperatureIChO
- Enzyme kinetics from elementary rate constantsUKChO Round 2 · IChO
Equilibrium
- pH of a weak acidA-Level (AQA) · C3L6 · UKChO Round 1 · IChO
- Buffer pH (Henderson–Hasselbalch)A-Level (AQA) · C3L6 · UKChO Round 1 · IChO
- Kp from KcUKChO Round 1 · UKChO Round 2 · IChO
- Solubility from KspC3L6 · UKChO Round 1 · IChO
- pH of a weak baseUKChO Round 1 · UKChO Round 2 · IChO
- Kc and its units for the Haber processA-Level (AQA)
- Kc from equilibrium amounts and volumeA-Level (AQA)
- Kc from initial amounts and one equilibrium amountA-Level (AQA)
- An equilibrium concentration from KcA-Level (AQA)
- Kp from equilibrium amounts and total pressureA-Level (AQA)
- Kp and its units for the Haber processA-Level (AQA)
- Ksp from a solubility in g dm⁻³UKChO Round 1
- Solubility with a common ionUKChO Round 1
- pH of benzoic acid from a weighed sampleC3L6 · UKChO Round 1 · IChO
- H₂ + I₂ ⇌ 2HI: equilibrium amountsC3L6 · UKChO Round 1 · IChO
Electrochemistry
- ΔG° from E°UKChO Round 1 · UKChO Round 2 · IChO
- Nernst equationUKChO Round 2 · IChO
- Mass deposited by electrolysisC3L6 · UKChO Round 1 · IChO
- E°cell from reduction potentialsA-Level (AQA) · C3L6 · UKChO Round 1 · IChO
- Equilibrium constant from E°cellUKChO Round 1
- Electrode potential away from standard conditionsUKChO Round 1
- Latimer diagram: skipping an oxidation stateUKChO Round 2 · IChO
- Disproportionation constant from a Latimer diagramUKChO Round 2 · IChO
- Daniell cell away from standard conditionsUKChO Round 2 · IChO
Spectroscopy & other
- Concentration from absorbanceC3L6 · UKChO Round 1 · IChO
- Wavelength to break a bondC3L6 · UKChO Round 1 · IChO
- Density of a rock-salt crystalUKChO Round 2 · IChO
- Atomic radius of a face-centred cubic metalUKChO Round 2 · IChO
- Atomic radius of a body-centred cubic metalUKChO Round 2 · IChO
- Unpaired electrons from a magnetic momentUKChO Round 2 · IChO
- Crystal field splitting from a d–d absorptionUKChO Round 2 · IChO
Stoichiometry
- Reacting masses: iron from iron(III) oxideA-Level (AQA)
- Percentage yield of an esterA-Level (AQA)
- Atom economyA-Level (AQA)
- Titration: sodium hydroxide against sulfuric acidA-Level (AQA)
- Back titration: purity of calcium carbonateA-Level (AQA)
- Volume of gas from a reacting massA-Level (AQA)
- Relative molecular mass of a volatile liquidA-Level (AQA)
- Water of crystallisationA-Level (AQA)
- Making and diluting a standard solutionA-Level (AQA)
- Number of atoms in a mass of compoundA-Level (AQA)
- Empirical formula from the masses of each elementA-Level (AQA)
- Oxygen content from combustion analysisUKChO Round 1
- Iron in a tablet by permanganate titrationUKChO Round 1
- Copper(II) by iodometric titrationUKChO Round 1
- Water hardness by EDTA titrationUKChO Round 2 · IChO
- Nickel by EDTA back titrationUKChO Round 2 · IChO