enthalpy definitions

Question 1

ionisation enthalpy

Answer 1

first ionisation energy = enthalpy change when each atom in one mole of gaseous atoms loses one electron to form one mole of gaseous 1+ ions eg. Mg(g) –> Mg+(g) + e-
second ionisation energy eg. Mg+(g) –> Mg2+ +e-
endothermic

Question 2

electron affinity

Answer 2

first electron affinity = enthalpy change when each atom in one mole of gaseous atoms gains one electron to form one mole of gaseous 1- ions (exothermic)
second affinity is endothermic

Question 3

enthalpy of atomisation

Answer 3

enthalpy change when one mole of gaseous atoms is produced from an element in its standard state eg. 1/2I2(s) –> I(g)
endothermic

Question 4

hydration enthalpy

Answer 4

enthalpy change when one mole of gaseous ions becomes hydrated (dissolved in water)
eg. Mg2+(g) + aq –> Mg2+ (aq)
exothermic

Question 5

enthalpy of solution

Answer 5

enthalpy change when one mole of an ionic solid dissolves in an amount of water large enough so that the dissolved ions are well separated and do not interact with each other eg. MgCl(s) + aq –> Mg2+(aq) + 2Cl-(aq)

Question 6

bond dissociation enthalpy

Answer 6

enthalpy change when one mole of covalent bonds is broken in the gaseous state
eg. I2(g) –> 2I(g)
endothermic

Question 7

lattice enthalpy of formation

Answer 7

enthalpy change when one mole of an ionic compound is formed from its constituent ions in the gas phase
eg. Mg2+ (g) + 2Cl- (g) –> MgCl2 (s)
exothermic

Question 8

lattice enthalpy of dissociation

Answer 8

enthalpy change when one mole of a solid ionic compound is broken up into its constituent ions in the gas phase
eg. MgCl(s) –> Mg2+(aq) + 2Cl-(aq)
endothermic

Question 9

enthalpy of vaporisation

Answer 9

enthalpy change when one mole of a liquid is turned to gas
eg. H20(l) –> H20(g)
endothermic

Question 10

enthalpy of fusion

Answer 10

enthalpy change when one mole of a solid is turned into a liquid
eg. Mg(s) –> Mg(l)
endothermic