topic 13

Question 1

lattice energy

Answer 1

• the energy change when one mole of an ionic solid is formed from its gaseous ions
• measure of ionic bond strength

Question 2

enthalpy of atomisation

Answer 2

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

Question 3

first electron affinity

Answer 3

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 single -1 charge

Question 4

second electron affinity

Answer 4

the enthalpy change when one mole of gaseous 1- ions gains one electron per ion to produce gaseous 2- ions

Question 5

is the first electron affinity exothermic or endothermic

Answer 5

exothermic for atoms that normally form negative ions because the ion is more stable than the atom

Question 6

is the second electron affinity exothermic or endothermic

Answer 6

endothermic because it takes energy to overcome the repulsive force between the negative ion and the electron

Question 7

first ionisation enthalpy

Answer 7

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

Question 8

second ionisation enthalpy

Answer 8

the enthalpy change to remove 1 mole of electrons from one mole of gaseous 1+ ions to produce one mole of gaseous 2+ ions

Question 9

effect of the size of ions on the lattice enthalpy

Answer 9

• 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

Question 10

effect of the charge of ions on the lattice enthalpy

Answer 10

• the bigger the charge of the ion, the greater the attraction between the ions so the stronger the lattice enthalpy (more negative values)

Question 11

enthalpy change of formation

Answer 11

the energy transferred when 1 mole of the compound is formed from its elements under standard conditions all reactants and products being in their standard states

Question 12

theoretical vs Born-Haber lattice enthalpies

Answer 12

• when a compound shows covalent character, the theoretical and the born Haber lattice enthalpies differ
• the more covalent character the bigger the difference between the values
• Born-Haber is the real experimental value

Question 13

what is meant by polarisation

Answer 13

• when the negative ion becomes distorted and more covalent

Question 14

100% ionic ions

Answer 14

• completely spherical
• theoretical and Born-Haber values will be the same

Question 15

ionic with covalent character

Answer 15

• charge cloud is distorted
• the theoretical and the experimental Born Haber lattice enthalpies will differ

Question 16

what causes polarising power to increase

Answer 16

• the positive ion is small
• the positive ion has multiple charges

Question 17

enthalpy of lattice formation

Answer 17

• standard enthalpy change when 1 mole of an ionic crystal lattice is formed from its constituent ions in gaseous form

Question 18

enthalpy of solution

Answer 18

standard enthalpy change when one mole of an ionic solid dissolves in a large enough amount of water to ensure that the dissolved ions are well separated and do not interact with one another

Question 19

enthalpy of hydration

Answer 19

• enthalpy change when one mole of gaseous ions
  become hydrated so that further dilution causes no further heat change
• always exothermic

Question 20

what does the strength of enthalpy of lattice formation depend on

Answer 20

• the size of the ions - larger the ion, the less neg the enthalpies of lattice formation (charges are further apart so weaker attractive force)
• the charges on the ion - bigger the charge, greater the attraction between the ions so the stronger the lattice enthalpy (more negative)

Question 21

enthalpy of solution formula

Answer 21

-H,le + sum of H,hyd

Question 22

is enthalpy of solution endothermic or exthothermic?

Answer 22

• endothermic
• substances in lattice must be broken up
• enthalpy of lattice dissociation = energy needed to break up the lattice

Question 23

what do ionic substances dissolve in

Answer 23

• only in polar solvents