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CAIE IGCSE Chemistry Enthalpy Change and Its Sign

CAIE IGCSE Chemistry Enthalpy Change and Its Sign
Cambridge IGCSE Chemistry 0620 syllabus for exams in 2026, 2027 and 20282026–2028

Practise defining reaction enthalpy change and using its sign to classify thermal energy transfer, with negative values for exothermic reactions.

How this is tested

  • define enthalpy change as the thermal energy transferred during a chemical reaction
  • use a negative enthalpy change for exothermic and a positive value for endothermic
  • connect the sign with whether bond formation releases more or less energy than bond breaking

Question 3(b)

[Maximum number: 1]

The symbol equation for the industrial production of ammonia is shown.

N2( g)+3H2( g)⇌2NH3( g)ΔH=−90 kJ/mol\mathrm{N}_{2}(\mathrm{~g})+3 \mathrm{H}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{NH}_{3}(\mathrm{~g}) \quad \Delta H=-90 \mathrm{~kJ} / \mathrm{mol}

State the meaning of ΔH\Delta H.