Key term
Edexcel A-Level Chemistry 9CH0
Atomic Structure and the Periodic Table
Bonding and Structure
Inorganic Chemistry and the Periodic Table
Topic overviewFlame tests and how they workThermal decomposition of nitrates and carbonatesCarrying out flame tests and testing the gasesGroup 2 elements and their compoundsTrends in Group 7 and predicting fluorine and astatineHalogen displacement reactionsDisproportionation and the reactions of chlorineHalides with concentrated sulfuric acid, and the hydrogen halidesTesting for halide ions with silver nitrateTesting for carbonate and hydrogencarbonate ionsTesting for sulfate and ammonium ions
Formulae, Equations and Amounts of Substance
Topic overviewThe mole, molar mass and empirical formulaThe ideal gas equation and molar volumeEquations, concentration and reacting quantitiesStandard solutions, titration and uncertaintyPercentage yield, atom economy and acid reactionsCore practicals 1 to 3Empirical formula and water of crystallisation by experimentApparatus, uncertainty and mathematical skills
Organic Chemistry I
Topic overviewFormulae, homologous series and functional groupsIUPAC nomenclatureTypes of organic reaction and structural isomerismStereoisomerism and E/Z nomenclaturePractical techniques in organic chemistryAlkanes, crude oil and combustion pollutantsRadical substitutionAlkenes, the double bond and hydrogenationElectrophilic addition, Markovnikov's rule and the test for an alkeneAddition polymers and waste polymersNucleophilic substitution of halogenoalkanesRates of hydrolysis and the SN1 and SN2 mechanismsClassifying and oxidising alcoholsAlcohols: practical techniques and the core practicals
Modern Analytical Techniques I
Energetics I
Kinetics I
Equilibrium I
Acid-Base Equilibria
Energetics II
Redox II
Transition Metals
Topic overviewElectron configuration and what makes a transition metalComplex ions, ligands and the colour of transition metal ionsCoordination number, monodentate ligands and the shapes of complexesBidentate and multidentate ligands, and ligand exchangeVanadium and chromium chemistryReactions with sodium hydroxide and ammoniaCobalt and copper complexesLigand exchange, amphoteric behaviour and the chelate effectTransition metals as catalysts
Kinetics II
Organic Chemistry II
Topic overviewChiralityAldehydes, ketones and their oxidationReduction and nucleophilic addition of HCNTesting for a carbonyl group: 2,4-DNPH and the iodoform reactionCarboxylic acids and their reactionsEsters and acyl chloridesReflux, extraction and recrystallisationDistillation, melting temperature and working safely
Organic Chemistry III
Topic overviewThe structure of benzene and the evidence for itElectrophilic substitution of benzeneNitration, halogenation, Friedel-Crafts and phenolAmines: structure and basicityReactions of amines and preparing themAmides and condensation polymersAmino acids, zwitterions and proteinsEmpirical and molecular formulae from analytical dataGrignard reagents and multi-step synthesisPurification techniques and the aspirin preparation
Energetics I
Hess's law and bond enthalpies
- 3 things to know
- Papers 1 and 3
Overview
Hess's law and cycles built from enthalpies of formation or combustion, bond and mean bond enthalpies and why calculations from them are approximate, and Core Practical 8 finding the enthalpy change for decomposing potassium hydrogencarbonate indirectly.
What you need to know
Answer each one before you reveal it.
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Key term
What physical state do bond enthalpy values assume?
Key term
State Hess's law.
Questions from this subtopic
Each one with the model answer underneath.
- 1
State Hess's law.
Model answer
The total enthalpy change of a reaction is independent of the route taken, provided the starting and finishing conditions are the same.
- 2
Why is Hess's law useful?
Model answer
It allows enthalpy changes that cannot be measured directly to be calculated from ones that can.
- 3
Given enthalpies of formation, how is ΔH for a reaction obtained?
Model answer
Sum of enthalpies of formation of the products minus the sum of enthalpies of formation of the reactants.
- 4
Given enthalpies of combustion, how is ΔH for a reaction obtained?
Model answer
Sum of enthalpies of combustion of the reactants minus the sum of enthalpies of combustion of the products.
- 5
In a Hess cycle built from enthalpies of formation, which way do the arrows point?
Model answer
From the elements up to the reactants and to the products (formation arrows point away from the elements).
- 6
In a Hess cycle built from enthalpies of combustion, which way do the arrows point?
Model answer
From the reactants and products down to the combustion products (arrows point towards CO₂ and H₂O).
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