Thermodynamics; Enthalpy change definitions

Enthalpy change: for a system is the heat taken in or given off during a chemical or physical change that takes place at a constant pressure.


Standard conditions:
-1 mole, mol-1
-100kpa
-298K
(if other temperature is used, will be stated next to the H in the sign for enthalpy change e.g. H1000)


Enthalpy of formation: the enthalpy change when one mole of a molecule is formed from its elements in their standard states. 

Enthalpy of atomisation: is the standard enthalpy change that accompanies the formation of one mole of gaseous atoms. 

Ionisation enthalpy: the standard change for the removal of one electron from a species in the gas phase to form a positive ion and an electron both also in the gas phase.  Mg --> Mg+ +e- 


Atomisation: change needed to produce 1 mole of atoms in their standard states, (half the value for Cl-Cl bond enthalpy) (g) molecules to (g) atoms.

Bond dissociation enthalpy: is the standard enthalpy change that accompanies the breaking of a covalent bond in a gaseous molecule to form two free radicals also in their gaseous phase.

Electron affinity: is the standard enthalpy change when an electron is added to an isolated atom in the gas phase.

Lattice enthalpy: the standard enthalpy change that accompanies the separation of one mole of a solid ionic lattice into its gaseous ions. 


Standard enthalpy of formation: is the enthalpy change involved in the production of one mole of a compound from its elements under standard conditions, with all products and reacants in their standard states.


Hess's Law: overall enthalpy change in a complete cycle must/ will be equal to 0.


First law of thermodynamics: energy can not be created or destroyed, but stored and transferred.