Chemistry - R1.2 Energy Cycles in reactions

Bond enthalpy

The energy required to break one mole of bonds by homolytic fission in one mole of gaseous covalent molecules under standard conditions

Derive from experimental data, bond enthalpies are average values

Bond enthalpy change calculation

Sum of bond broken - sum of bond formed

Hess’s law

Regardless of the routes by which a chemical reaction proceeds, the enthalpy change will always be the same, as long as the initial & final states of the system are the same.

Enthalpy change of A → B

= sum of enthalpy change of A→ C and C→ B

Standard enthalpy change of formation

The energy change that occurs when one mole of a substance is formed from its constituent elements in their standard states.

Standard enthalpy change of combustion

The enthalpy change that occurs when one mole of a substance in its standard state is burned completely in oxygen.

Born-Haber cycle

An application of Hess’s law, used to show energy changes in the formation of an ionic compound

Ionization energy

The standard enthalpy change that occurs on the removal of one mole of electrons from one mole of atoms or positively charged ions in the gaseous state.

Enthalpy of atomization

The standard enthalpy change that occurs when one mole of gaseous atoms of an element is formed

Electron affinity

The standard enthalpy change on the addition of one mole of electrons to one mole of atoms in the gaseous state

Lattice enthalpy

The standard enthalpy change that occurs when gaseous ions are formed from one mole of structural units of a solid ionic lattice