Summary ALEVEL CHEMISTRY - Enthalpy Changes Notes and Definitions

Enthalpy Changes
enthalpy change is the heat energy transferred in a reaction at constant pressure.
Enthalpy change the enthalpy change when 1 mole of a compound is formed from its
of formation elements in their standard states under standard conditions
2C(s) + 3H2 (g) + 1/2O2(g) ---> C2H5OH
Enthalpy of the enthalpy change when 1 mole of aqueous ions formed from 1 mole
hydration of gaseous ions
Na+ (g) --> Na+(aq)
Enthalpy change the enthalpy change when 1 mole of solute is dissolved in enough
of a solution solvent so there is no further enthalpy change on further dilution
NaCl(s) ---> NaCl(aq)
Enthalpy change the enthalpy change when 1 mole of gaseous atoms is formed from an
of atomisation of element in standard state
an element 1/2Cl2 (g) ---> Cl(g)
Enthalpy change the enthalpy change when 1 mole of a compound in standard state is
of atomisation of converted to gaseous atoms
a compound NaCl(s) ---> Na(g) + Cl(g)
Bond dissociation the enthalpy change when all the bonds of the same type in 1 mole of
enthalpy gaseous molecules are broken
Cl2(g) ---> 2Cl(g)
First ionisation the enthalpy change when 1 mole of gaseous 1+ ions is formed from 1
energy mole of gaseous atoms
Mg(g) ---> Mg+(g) + e-
Second ionisation the enthalpy change when 1 mole of gaseous 2- ions is formed from 1
energy mole of gaseous 1- ions
O-(g) + e- ---> O2-(g)

First electron the enthalpy change when 1 mole of gaseous 1- ions is formed from 1
affinity mole of gaseous atoms
O(g)+ e- ---> O-(g)