IB›IB Chemistry HL›Mind mapsR1.1 Measuring enthalpy changesIB Chemistry HL: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsSystem, surroundingsSystem = reacting chemicals; rest is surroundingsTotal energy is conservedTemperature = average kinetic energyHeat = energy transferred by temperature differenceExo and endoExothermic: system to surroundings, ΔH negativeSurroundings warm up in exothermicEndothermic: surroundings to system, ΔH positiveEndothermic example: dissolving NH₄NO₃Exothermic example: neutralisationEnergy profilesMore stable products: energy releasedExothermic: products below reactantsEndothermic: products above reactantsHump height = activation energyEndothermic: Ea>E_a >Ea> ΔHEnthalpy changesmeasuring energyΔHJkJKStandard ΔHHeat at constant pressureStandard: 100 kPa, 1 mol dm⁻³, standard statesUsually quoted at 298 KUnits kJ mol⁻¹ with signCalorimetryQ=mcΔTQ = mc\Delta TQ=mcΔTccc of water = 4.18 J g⁻¹ K⁻¹Find moles of limiting reactantΔH=−Qn\Delta H = -\frac{Q}{n}ΔH=−nQ in kJHCl + NaOH, ΔT 6.6 K: −55.2 kJ mol⁻¹Exam tipsThermometer measures surroundings, not systemUse total mass of solutionExperimental values less exothermic: heat lossAlso incomplete combustion, evaporation of fuelInsulate, lid and stir to cut error