chapter 5: energetics Flashcards
definition of standard enthalpy change of reaction
energy change when molar quantities of reactants as stated in the thermochemical equation react together under standard conditions
what are the standard conditions
298K
1 bar
definition of standard enthalpy change of neutralisation
energy change evolved when one mole of water is formed during neutralisation of an acid and an alkali under standard conditions (always exothermic)
why is the enthalpy change of neutralisation less exothrmic than -57kJmol-1
part of the enthalpy evolved is used to dissociate the remaining acid completely
definition of standard enthalpy change of combustion
energy evolved when one mole of substance is completely burned in excess oxygen under standard conditions
definition of enthalpy change of atomisation of elements
energy absorbed when one mole of gaseous atoms is formed from its element under standard conditions (always endothermic)
definition of standard enthalpy change of atomisation of compounds
energy absorbed when one mole of a compound is converted to its constituent gaseous atoms under standard conditions
definition of standard bond dissociation energy
energy needed to break one mole of covalent bonds between two atoms in the gaseous state under standard conditions (always positive)
definition of first ionisation energy
energy absorbed when one mole of electrons is removed from one mole of gaseous atoms to form one mole of singly charged gaseous cation (1st I.E. is always positive)
definition of first electron affinity
energy change when one mole of electron is added to one mole of gaseous atoms to form one mole of singly charge gaseous anions (1st E.A is negative)
why are subsequent EA positive
energy is needed to overcome the repulsion between the incoming electron and the negatively charged anion
definition of standard lattice energy
energy evolved when one mole of an ionic compound is formed from its constituent gaseous ions under standard conditions
definition of standard enthalpy change of hydration
energy evolved when one mole of gaseous ions is surrounded by water molecules, forming a solution at infinite dilution under standard conditions (always negative)
equation for hydration energy
ionic charge/ionic radius
definition of enthalpy change of solution
energy change when one mole of substance is dissolved by solvent such that further dilution produces no more energy change under standard conditions
