topic 13- further energetics

The energy change when one mole of an ionic solid is formed from its gaseous ions The value of the lattice energy depends on: -Magnitude of charge of ions -Ionic radii -Lattice structure -Extent of covalent character in the bond.

The standard enthalpy change when one mole of gaseous atoms are formed from an element in its standard state, at a stated temperature and 100kPa. In equation form: Mg(s) → Mg(g) S8(s) → 8S(g) ½ N2 (g) → N(g) ½ Cl2(g) → Cl(g)

The first electron affinity Eea(1) is the energy change when each atom in a mole of atoms in the gaseous state gains an electron and forms a 1- ion. In equation form: N (g) + e → N- (g) S (g) + e → S- (g) First electron affinity is negative (exothermic) except for noble gases, where the ‘new’ electron must go into an new shell

The second electron affinity is when a mole of 1- ions gains a second electron and forms a 2- ion. In equation form: N- (g) + e → N2- (g) S- (g) + e → S2- (g) Second electron affinity is positive (endothermic) due to the already negatively charged ion repelling the incoming electron.

Assume: - ions are in contact - ions are perfect spheres - even distribution of charge throughout the volume

ionic bonding model is not sufficient due to the extent of covalent character bigger discrepancy the bigger the extend of character

measure of the degree of randomness or disorder of particles higher entropy - highest disorder moles of products > moles of reactants - positive entropy for feasible reaction -both entropy of surroundings and system is positive because more way the particles can be arranged

endothermic reaction Ba(OH)2.8H2O (s) + 2NH4Cl (s) → BaCl2 (s) + 10 H2O (l) + 2 NH3 (g) entrophy change is positive thermodynamically spontaneous

endothermic 2 CH3COOH (l) + (NH4)2CO3 (s) → 2 CH3COONH4 (aq) + H2O (l) + CO2 (g) entrophy change is positive thermodynamically spontaneous

exothermic reaction 2 Mg (s) + O2 (g) → 2 MgO (s) entropy is positive as the surroundings overpowers thermodynamically spontaneous

entropy of surroundings + entropy of system

products - reactants

-enthlapy change / temperature

Calculate whether a reaction is feasable (spontaneous): - If feasible gibbs is -ve - If not feasible its +ve - If equilibrium its 0 enthlapy change - temp(entropy change)

Make ΔG=0 Rearrange equation enthlapy change / entropy of system

• charge • ionic radius

mostly 100% ionic

differing charges and ionic radius so one polarises the other so bonding has covalent character

increase number of moles change of state - s - l - g

the enthlapy change when one mol of an ionic solid dissolves in water to form an infinitely dilute solution

enthlapy change when one mole of an ion in its gaseous state is completely hydrated by water

ΔG = -RTlnK

kintetic stability -if thermodynamically feasable dosent necisary mean it will occur activation energy too high non standard conditions -may not happen at standard conditions may need to be heated

if gibs of solution is negative the products are favoured at equilibrium and the salt is soluble if the gibs of solution is positive than the solid salt is favoured at equilibrium so the salt is insoluble