energetics 2 - lattice energy Flashcards
Enthalpy change of formation
The standard enthalpy change of formation of a compound is the energy transferred when 1 mole of the compound is formed from its elements under standard conditions (298K and 100kpa), with all reactants and products being in their standard states
Enthalpy of atomisation
The enthalpy of atomisation of an element is the enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard state
First lonisation enthalpy
The first ionisation enthalpy is the enthalpy change required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous ions with a +1 charge
Second lonisation enthalpy
The second ionisation enthalpy is the enthalpy change to remove 1 mole of electrons from one mole of gaseous 1+ ions to produces one mole of gaseous 2+ ions.
First Electron Affinity
The first electron affinity is the enthalpy change that occurs when 1 mole of gaseous atoms gain 1 mole of electrons to form 1 mole of gaseous ions with a -1 charge
is the first electron affinity endothermic or exothermic?
The first electron affinity is exothermic for atoms that normally form negative ions because the ion is more stable than the atom and there is an attraction between the nucleus and the electron
Second Electron Affinity
The second electron affinity is the enthalpy change when one mole of gaseous 1- ions gains one electron per ion to produce gaseous 2- ions
is the second electron affinity exothermic or endothermic?
The second electron affinity for oxygen is endothermic because it take energy to overcome the repulsive force between the negative ion and the electron
do first Electron affinity values will become more or less exothermic as you go down Group 7 from chlorine to iodine ?
why?
First Electron affinity values will become less exothermic as you go down Group 7 from chlorine to iodine because the atoms get bigger and have more shielding so it becomes less easy to attract electrons to the atom to form the negative ion
Enthalpy of lattice formation
The Enthalpy of lattice formation is the standard enthalpy change when 1 mole of an ionic crystal lattice is formed from its constituent ions in gaseous form
The strength of an enthalpy of lattice formation depends on… (2)
- The sizes of the ions
- The charges on the ion
how does the size of the ions affect the strength of a enthalpy of lattice formation?
The larger the ions, the less negative the enthalpies of lattice formation (i.e. a weaker lattice). As the ions are larger the charges become further apart and so have a weaker attractive force between them.
how do the charges of the ions affect the strength of a enthalpy of lattice formation?
The bigger the charge of the ion, the greater the attraction between the ions so the stronger the lattice enthalpy (more negative values).
lattice enthalpies down a group
The lattice enthalpies become less negative down any group. e.g. LiCi, NaCI, KCI, RbCl
Theoretical lattice enthalpies assumes a…
perfect ionic model where the ions are 100% ionic and spherical and the attractions are purely electrostatic