topic 13: energetics II

Question 1

what is the enthalpy change of formation

Answer 1

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

Question 2

what is the enthalpy change of atomisation

Answer 2

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

Question 3

what is the first ionisation energy

Answer 3

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-

Question 4

what is the equation for second ionisation energy

Answer 4

X+(g) —-> X2+(g) + e-

Question 5

what is the first electron affinity

Answer 5

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)

Question 6

what is the equation for the second electron affinity

Answer 6

X-(g) + e- —-> X2-(g)

Question 7

what is the term lattice energy

Answer 7

the energy change when one mole of an ionic solid id formed from its gaseous ions under standard conditions

Question 8

what does the strength of the lattice formation depend on

Answer 8

the size and charge of the ion

Question 9

explain how the size of an ion affects the strength of the lattice formation

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

explain how the size of an ion affects the strength of the lattice formation

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

what does the theoretical lattice enthalpies assume

Answer 11

it assumes that the ions are 100% ionic and
spherical and the attractions are purely electrostatic.

Question 12

what does a large difference between the theoretical and Born Haber lattice enthalpy suggest

Answer 12

that it has covalent character

Question 13

when does the polarising power of cation increase

Answer 13

when they are small and have a high charge

Question 14

what does the polarisability of an anion depend on. explain

Answer 14

size - the bigger the ion the more easily it is distorted

Question 15

what is polarisation

Answer 15

the distortion of an anion’s electron cloud by a cation

Question 16

what is polarisability

Answer 16

the tendency of an anion’s electron cloud to be distorted by a cation - that has a polarisability

Question 17

what is polarising power

Answer 17

the ability for a cation to distort an anion’s electron cloud

Question 18

what does the most exothermic enthalpy change of formation mean

Answer 18

it is the most thermodynamically stable

Question 19

what is the enthalpy change of solution

Answer 19

enthalpy change when one mole of an ionic substance dissolves in water to give a solution of infinite dilution

Question 20

what is the enthalpy change of hydration

Answer 20

enthalpy change when one mole of gaseous ions dissolve in sufficient water to give an infinitely dilute solution (always negative)

Question 21

what is the enthalpy change of lattice formation

Answer 21

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