Energetics Definitions

exothermic

gives out heat as bonds formed, -ve enthalpy

endothermic

takes in heat as bonds broken, +ve enthalpy

internal energy

the sum of the kinetic energies of all the chemical species within the system (the energy due to movement of all species) and the sum of the potential energies (the energy stored within the chemical bonds) of all the chemical species within the system

standard enthalpy change (of a reaction)

the change in heat energy content when molar quantities of the reactants are reacted together under standard conditions (100kPa, 298K)

standard conditions

1 atm, 298K, 1M

standard enthalpy change of combustion

the change in heat energy content when one mole of the substance is burnt completely, in excess oxygen, under standard conditions (100kPa and 298K)

standard enthalpy change of formation

the change in heat enrgy content when one mole of the substance is formed from its elements in their standard states, under standard conditions (100kPa and 298K)

hess's law

if a reaction can take place by more than one route, the overall enthalpy change for each route is the same irrespective of the route taken provided that the initial and final conditions are the same

enthalpy of atomisation/sublimation

the energy required to form one mole of atoms of an element in the gas state from the element in its usual state at 298K and 1 atm

enthalpy of ionisation

the energy required to remove the least firmly held electron from one mole of atoms of an element in the gas state

electron affinity

the energy charge when one mole of (singly) charged anions is formed from one mole of atoms in the gas state

enthalpy of formation

the energy change when one mole of substance is formed from its constituent elements in their standard states at 298K and 1 atm

lattice formation enthalpy

the enthalpy change when one mole of an ionic lattice is formed from its isolated gaseous ions (exothermic)

lattice dissociation enthalpy

the enthalpy change when one mole of an ionic lattice dissociates into isolated gaseous ions (endothermic)

charge density

charge/volume

enthalpy of solution

the energy change when 1 mole of an ionic solid is dissolved in sufficient solvent to give an infinitely dilute solution

hydration enthalpy

the energy change when 1 mole of gaseous ions is dissolved in sufficient solvent to give an infinitely dilute solution

bond enthalpy

the energy needed to break one mole of bonds in the substance in the gaseous state