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Browse all science resourcesUse forces, molecular models and energy arguments to explain why breaking bonds requires energy and forming bonds releases it. Students connect individual bond changes with the overall energy balance of a reaction.
Draw molecular structures, count bonds accurately and use average bond enthalpies to estimate reaction enthalpy. Guided practice focuses on clear bond tallies, coefficients and sign conventions.
Introduce Hess’s law through reactions that are difficult to measure directly. Students construct energy cycles and combine reaction equations to determine an unknown enthalpy change.
Develop precision in defining standard enthalpies of formation and combustion, writing the corresponding equations and interpreting data-booklet values. Students check amounts, states and reference conditions.
Build Hess cycles using formation data and connect the cycle to a systematic calculation method. Students track species, coefficients, values and signs, then compare routes to the same enthalpy change.
Use combustion data to calculate reaction enthalpy and explain the direction of the subtraction from the energy cycle. Students distinguish formation and combustion methods before choosing a calculation route.
Construct Born-Haber cycles from individual energy steps. Students connect atomisation, bond dissociation, ionisation, electron affinity and lattice enthalpy, checking species, states and signs throughout.
Calculate unknown energy changes using Born-Haber cycles and a step-by-step audit. Students then explain lattice-enthalpy trends using ionic charge and size, linking quantitative results to structure.
Use hot and cold reactions to distinguish the system from its surroundings, explain energy conservation, and classify endothermic and exothermic changes.
Connect thermometer observations, energy-transfer directions and energy profiles. Students practise the sign of enthalpy change, enthalpic stability, graph interpretation and error correction.
