13.1

Question 1

define standard lattice energy

Answer 1

the energy change when one mole of the ionic solid is formed from its gaseous ions under standard conditions of 100kPa and a stated temperature

Question 2

what factors effect standard lattice energy

Answer 2

number of ions in the compound - the more ions in a molecule the more negative the lattice energy
the amount of cation to anion interactions - the more interactions the more negative the lattice energy
the sum of their atomic radii - smaller atomic radius the more negative the lattice energy

Question 3

define standard enthalpy change of atomisation

Answer 3

enthalpy change measured under standard conditions of a stated temperature and 100kPa when one mole of gaseous atoms is formed from an element in its standard state

Question 4

what is the equation for standard lattice energy of NaCl

Answer 4

Na+(aq) + Cl-(aq) -> NaCl(s)

Question 5

what is the equation for standard enthalpy change of atomisation of chlorine and sodium

Answer 5

1/2Cl2(g) -> Cl(g)
Na(s) -> Na(g)

Question 6

define first electron affinity

Answer 6

the energy change when each atom in a mole of atoms in the gaseous state gains an electron to form a 1- ion

Question 7

what is the equation for the first electron affinity of chlorine

Answer 7

Cl(g) + e- -> Cl-(g)

Question 7

in general are first electron affinities positive or negative and why are noble gases an exception

Answer 7

first electron affinity is usually negative but noble gases are positive because of the repulsion caused by the electrons in the outer shell mean that an additional electron would have to occupy a new valence shell

Question 8

in general are the second electron affinities positive or negative

Answer 8

positive

Question 9

what is the equation for the second electron affinity of oxygen

Answer 9

O-(g) + e- -> O^2-(g)

Question 10

what assumptions are made in calculating lattice energy

Answer 10

ions are in contact with one another
ions are perfectly spherical
the charge of an ion is evenly distributed around the center so each ion can be considered as point charges

Question 11

what could cause the experimental value for lattice energy to be more negative than the expected value

Answer 11

if the bonding in the lattice has considerable covalent character

Question 12

what is covalent character

Answer 12

covalency in bonding is caused by polarization of the anion by the cation which results in distortion of the electron density within the anion resulting in a higher electron density near the cation

Question 13

what are fajans rules for the extent of polarisation of an anion

Answer 13

polarisation will be increased by:
a high charge and small size cation
a high charge and large size anion

Question 14

what is polarising power

Answer 14

the ability of a cation to attract electrons from the anion

Question 15

what increases a cations polarising power and how can it be measured

Answer 15

high charge
small radius
by calculating charge density

Question 16

define enthalpy change of solution

Answer 16

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

Question 17

what is the equation for the enthalpy change of solution of sodium chloride

Answer 17

NaCl(s) -(aq)-> Na+(aq) + Cl-(aq)

Question 18

is dilution and endo or exothermic process and why

Answer 18

it is an endothermic process as ions in solution move further apart

Question 19

what is #solH and how can it be found

Answer 19

refers to an infinitely dilute solution
found through extrapolation

Question 20

what is the point of infinite dilution

Answer 20

the point at which further dilution has no measurable effect on #solH

Question 21

define enthalpy change of hydration

Answer 21

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

Question 22

is hydration an exo or endothermic process

Answer 22

exothermic

Question 23

what is the equation for enthalpy change of hydration for chlorine

Answer 23

Cl-(g) -(aq)-> Cl-(aq)

Question 24

how can water interact with the cations in solution

Answer 24

the dipole negative oxygen have an ion-dipole attraction which in some cases (often transition metals) can become a dative bond with the lone pair of electrons form the oxygen

Question 25

how can water interact with the anions in solution

Answer 25

the dipole positive hydrogen have ion-dipole interactions which can form hydrogen bonds using the anions lone pair of electrons (e.g. chlorine)

Question 26

what factors effect the value of the hydration enthalpy and why

Answer 26

increased charge = more negative hydration enthalpy as the ion has stronger interactions with the water molecules therefor there are stronger electrostatic forces of attraction between them
increased atomic radius = less negative hydration enthalpy because as ions become larger the electrostatic force of attraction between them decreases

Question 27

what is the trend in hydration enthalpy going down a group

Answer 27

hydration enthalpy becomes less negative due to an increase in atomic radius

Question 28

how does charge density effect hydration enthalpy

Answer 28

the greater the charge density the more negative the hydration enthalpy