Thermodynamics

Question 1

Lattice dissociation enthalpy is:

Answer 1

endothermic
energy needs to be put in to overcome the ionic attractions

Question 2

Enthalpy of hydration:

Answer 2

is exothermic
new attractions are formed (betw/ partial charges on h2o and ions, so energy released)
eg: Na+ (g) -> Na+ (aq)

Question 3

enthalpy of solution definition

Answer 3

enthalpy change when 1 mole of an ionic substance dissolves in enough solvent to form an infinitely dilute solution
eg: NaCl(s) –> Na+ (aq) + Cl- (aq)

Question 4

lattice dissociation enthalpy definition

Answer 4

enthalpy change when 1 mole of an ionic solid is fully dissociated into gaseous ions
eg: NaCl(s) –> Na+ (g) + Cl- (g)

Question 5

enthalpy of hydration

Answer 5

enthaply change when 1 mole of aqueous ions is formed from gaseous ions
(sum of individual hydration enthalpies)

Question 6

enthalpy of atomisation definition

Answer 6

enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard state

Question 8

atomisation of Cl2 from BD of Cl2

Answer 8

BD / 2

Question 9

Why is the enthalpy of hydration of Fl- ions more negative than the enthalpy of hydration of Cl- : (2)

Answer 9

• Fl- has smaller ionic radius / higher charge density
• stronger attraction betw/ Fl- ions and partial +ve of H