IGCSE›Cambridge IGCSE Chemistry›Mind mapsExothermic and Endothermic ReactionsCambridge IGCSE Chemistry: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsTwo typesExothermic transfers energy TO the surroundingsSurroundings warm upEndothermic takes energy FROM the surroundingsSurroundings cool downExothermic: combustion, neutralisation, respirationEnthalpy changeΔH is the energy transferred, in kJ/molNegative ΔH means exothermicPositive ΔH means endothermicCHX4\ce{CH4}CHX4 combustion: ΔH=−890 kJ/mol\Delta H = -890\,\text{kJ/mol}ΔH=−890kJ/molActivation energyMinimum energy colliding particles need to reactMeasured from reactants to the peakΔH is the gap from reactants to productsCatalysts lower Ea but not ΔHEnergeticsexo and endothermicΔHkJ/molEaBondsBreaking bonds takes in energyMaking bonds releases energyExothermic: more energy released making than breakingEndothermic: more energy needed to break bondsBond energy sumsΔH=broken−made\Delta H = \text{broken} - \text{made}ΔH=broken−madeHX2+ClX2→2 HCl\ce{H2 + Cl2 -> 2HCl}HX2+ClX22HClBroken: 432+244=676 kJ/mol432 + 244 = 676\,\text{kJ/mol}432+244=676kJ/molMade: 2×432=8642 \times 432 = 8642×432=864ΔH=676−864=−188 kJ/mol\Delta H = 676 - 864 = -188\,\text{kJ/mol}ΔH=676−864=−188kJ/molExam tipsAlways give the sign and units of ΔHHot vessel means exothermic, surroundings warm upShow working: bonds broken, bonds made, subtractBreaking bonds never releases energy