Standard Enthalpy change definitions 

Hess’ Law = the enthalpy change for any reaction is independent of the route taken from reactants to products providing starting and final conditions are the same.

Standard enthalpy change of formation = the enthalpy change when one mole of a compound is formed from its elements in their standard states, under standard conditions

Standard enthalpy change of atomisation =the enthalpy change when one mole of gaseous atoms forms from the element in its standard state (not in standard conditions)

Standard enthalpy change of solution = the enthalpy change when one mole of a compound is completely dissolved in water under standard contusions

Standard enthalpy change of hydration = the enthalpy change when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions

Standard enthalpy change of neutralisation = the enthalpy change when an acid is neutralised by a base to form one mole of water under standard contains (nearly always exothermic)

Standard enthalpy change of combustion =the enthalpy change when one mole of substance burns completely in oxygen under standard conditions (always exothermic)

Standard enthalpy change of reaction = the enthalpy change when the molar quantities of reactants as stated in the equations react under standard conditions

Bond enthalpy = the energy required to break 1 moles of covalent bonds in the gas states

Mean bond enthalpy = the mean bond enthalpy of the X-Y bonds is the mean value of the bond enthalpy values from the X-Y bond averaged across a wide range of compounds

Activation energy = the minimum energy required by the colliding particles for them to react successfully

Enthalpy = is the amount of chemical energy in the system that can be converted to heat energy