Definitions: Enthalpy changes

For the following, let AB represent a compound

* ‘The energy change when…’

Lattice Enthalpy

*… 1 mole of an ionic compound is formed from its gaseous ions under STP (298K, 100kPa).

Always exothermic

*… 1 mole of compound is formed from its constituent elements in their standard state.

Usually exothermic.

*… 1 mole of gaseous atoms are formed from the element in its standard state.

Always endothermic (bonds are broken)

*… 1 mole of gaseous 1+ ions is formed from gaseous atoms

Always endothermic (an electron overcomes the attraction from the nucleus)

*… mole of gaseous 2+ ions forms from 1 mole gaseous 1+ ions

Always endothermic (electron overcomes nuclear attraction)

*… 1 mole of gaseous 1- ions forms from gaseous atoms

Exothermic (electron attracted to the outer shell by the nucleus)

*… 1 mole of gaseous 2- ions forms from 1 mole gaseous 1- ions

Endothermic (arriving electron is repelled)

*… 1 mole of a compound is dissolved in water under standard conditions

Can be endothermic or exothermic

*… 1 mole of aqueous ions are formed from their gaseous ions under standard conditions

Exothermic process