IB Chemistry HL 100113

Bond-breaking absorbs and bond-forming releases energy.

Calculate the enthalpy change of a reaction from given average bond enthalpy data.

Include explanation of why bond enthalpy data are average values and may differ from those measured experimentally.

Average bond enthalpy values are given in the data booklet.

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, $ΔH_c^{⦵}$, and formation, $ΔH_f^{⦵}$, data are used in thermodynamic calculations.

Deduce equations and solutions to problems involving these terms.

Enthalpy of combustion and formation data are given in the data booklet.

An application of Hess’s law uses enthalpy of formation data or enthalpy of combustion data to calculate the enthalpy change of a reaction.

Calculate enthalpy changes of a reaction using $ΔH_f^{⦵}$ data or $ΔH_c^{⦵}$ data:

$ΔH^{⦵} = Σ(ΔH_f^{⦵}\text{products}) - Σ(ΔH_f^{⦵}\text{reactants})$

$ΔH^{⦵} = Σ(ΔH_c^{⦵}\text{reactants}) - Σ(ΔH_c^{⦵}\text{products})$

The equations to determine the enthalpy change of a reaction using ΔHf⦵ data or ΔHc⦵ data are given in the data booklet.

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: ionization energies, enthalpy of atomization (using sublimation and/or bond enthalpies), electron affinities, lattice enthalpy, enthalpy of formation.

The construction of a complete Born–Haber cycle will not be assessed.