topic 13: energetics II
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what is the enthalpy change of formation
the energy transferred when 1 mole of the compound is formed from its elements under standard conditions (298K and 100kpa), all reactants and products being in their standard states
what is the enthalpy change of atomisation
the enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard state under standard conditions
what is the first ionisation energy
the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous +1 ions. X(g) —-> X+(g) + e-
what is the equation for second ionisation energy
X+(g) —-> X2+(g) + e-
what is the first electron affinity
the energy released when one mole of electrons are added to one mole of gaseous atoms to form one mole of gaseous -1 ions. X(g) + e- —-> X-(g)
what is the equation for the second electron affinity
X-(g) + e- —-> X2-(g)
what is the term lattice energy
the energy change when one mole of an ionic solid id formed from its gaseous ions under standard conditions
what does the strength of the lattice formation depend on
the size and charge of the ion
explain how the size of an ion affects the strength of the 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
explain how the size of an ion affects the strength of the 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
what does the theoretical lattice enthalpies assume
it assumes that the ions are 100% ionic and spherical and the attractions are purely electrostatic.
what does a large difference between the theoretical and Born Haber lattice enthalpy suggest
that it has covalent character
when does the polarising power of cation increase
when they are small and have a high charge
what does the polarisability of an anion depend on. explain
size - the bigger the ion the more easily it is distorted
what is polarisation
the distortion of an anion’s electron cloud by a cation
what is polarisability
the tendency of an anion’s electron cloud to be distorted by a cation - that has a polarisability
what is polarising power
the ability for a cation to distort an anion’s electron cloud
what does the most exothermic enthalpy change of formation mean
it is the most thermodynamically stable
what is the enthalpy change of solution
enthalpy change when one mole of an ionic substance dissolves in water to give a solution of infinite dilution
what is the enthalpy change of hydration
enthalpy change when one mole of gaseous ions dissolve in sufficient water to give an infinitely dilute solution (always negative)
what is the enthalpy change of lattice formation
the standard enthalpy change when 1 mole of an ionic crystal lattice is formed from its constituent ions in gaseous form