International Baccalaureate IB Chemistry

Bond‑breaking absorbs and bond‑forming releases energy. Calculate the enthalpy change of a reaction from given average bond enthalpy data.

Hess’s law states that the enthalpy change for a reaction is independent of the pathway between the initial and final states.

Apply Hess’s law to calculate enthalpy changes in multistep reactions.

Standard enthalpy changes of combustion ($\Delta H_c^\circ$) and formation ($\Delta H_f^\circ$) data are used in thermodynamic calculations.

Deduce equations and solve problems involving these terms.

Calculate enthalpy changes of a reaction using $\Delta H_f^\circ$ data or $\Delta H_c^\circ$ data: $\Delta H^\circ = \sum \Delta H_f^\circ(\text{products}) - \sum \Delta H_f^\circ(\text{reactants})$ or $\Delta H^\circ = \sum \Delta H_c^\circ(\text{reactants}) - \sum \Delta H_c^\circ(\text{products})$.

A Born–Haber cycle is an application of Hess’s law, used to show energy changes in the formation of an ionic compound.

Interpret and determine values from a Born–Haber cycle for compounds composed of univalent and divalent ions. 

The cycle includes ionisation energies, atomisation enthalpy, electron affinities, lattice enthalpy and enthalpy of formation.