1.2 Energy cycles

Objective notes

5 learning objectives

1.2.1Bond energies

• Bond-breaking absorbs energy

• Bond-forming releases energy

• Calculate enthalpy change from average bond enthalpies

1.2.2Hess's law

• Enthalpy change independent of pathway

• Apply Hess's law to multistep reaction cycles

1.2.3(HL)—Standard enthalpy changes

• Combustion: ΔHc⦵

• Formation: ΔHf⦵

• Deduce equations and solve problems using standard enthalpy data

1.2.4(HL)—Hess's law applications

• ΔH⦵ = ΣΔHf⦵(products) − ΣΔHf⦵(reactants)

• ΔH⦵ = ΣΔHc⦵(reactants) − ΣΔHc⦵(products)

1.2.5(HL)—Born-Haber cycle

• Energy changes in ionic compound formation

• Univalent and divalent ions

• Interpret and determine cycle values; include lattice enthalpy and electron affinity terms