Lattice Enthalpy

Question 1

Lattice energy

Answer 1

Lattice energy is the enthalpy change when 1 mole of ionic compound is formed from it’s element under standard condition.

Question 2

Enthalpy change of atomisation

Answer 2

Enthalpy change of atomisation is the enthalpy change when 1 mole of gaseous atom is formed from it’s element under standard condition.

Question 3

Enthalpy change of solution

Answer 3

The energy absorbed or released when 1 mole of ionic solid dissolves in sufficient water to form a very dilute solution.

Question 4

Enthalpy change of hydration

Answer 4

The enthalpy change when 1 mole of specified gaseous ion dissolves in sufficient water to form a very dilute solution.

Question 5

First electron affinity

Answer 5

the enthalpy change when 1 mole of electron is added to gaseous atom to form 1 mole of gaseous 1-ions under standard conditions.

Question 6

What affects electron affinity?

Answer 6

Atomic size: Larger the size of atom , larger the distance between nucleus and incoming electron is more . Thus smaller will the force of attraction between nucleus and the incoming electrons .So the value of electron affinity will be lower

nuclear charge: greater the nuclear charge, the attraction between the nucleus and incoming electron will be greater. So, the value of electron affinity will be larger.

Electronic configuration: Stable the configuration of an atom, lesser will be it’s tendency to accept an electron and hence the value of electron affinity will be lower

Question 7

Variation of Ea in group 16 and 17

Answer 7

As we move down in Group 16 and 17 the value of electron affinity decreases as the size of atom increases so there will be less tendency to pull the incoming electrons as the force of attraction with the nucleus and incoming electron will be less.

Group 17 have higher value of electron affinity than group 16 because halogens have smaller atomic size and more nuclear charge than the members of group 16

Question 8

Thermal stability of Group 2 carbonates and nitrates

Answer 8

As we move down the group in group 2 carbonate and nitrate thermal stability increases as

1. size of cation increases
2. charge density of cation decreases
3. polarising capacity of cation decreases.
4. polarisation and distortion of anion decreases

Question 9

Solubility of group 2 Sulphates

Answer 9

As we move down the group in group 2 sulphates , solubility decreases as :

1. the decrease in the value of standard enthalpy change of hydration is more than
2. the decrease in the value of lattice enthalpy
3. so. solubility will be less exothermic

Question 10

Factors affecting lattice enthalpy and enthalpy change of hydration

Answer 10

Size of ion: smaller size, more exothermic

charge of iron :more charge, more exothermic

Question 11

ΔH solubility when +ve and -ve

Answer 11

more exothermic(-ve) : more soluble in water ; less soluble in hot water
more endothermic(+ve) : Less level in water ; more soluble in hot water

Question 12

Enthalpy change cycle

Answer 12

ΔH sol= ΔH hyd + ΔH hyd - ΔH latt

Question 13

Entropy

Answer 13

Entropy of a given system is the number of possible arrangements of particles and their energy in a given system.

Question 14

Factors affecting entropy

Answer 14

State
gas has higher entropy than liquid and liquid has higher entropy than solid

hardness
softer substances have higher entropy than the harder substances

number of atoms
the substance with more number of atoms in the molecule have higher entropy than the substance with less number of atoms in the molecule

number of moles
more number of moles the entropy will be higher

Question 15

Gibbs free energy

Answer 15

ΔG = ΔH – TΔS

if delta G is negative : the reaction is spontaneous
if the G is positive: the reaction is non spontaneous