Energetics II

Question 1

what’s the standard lattice energy

2

Answer 1

energy change when one mole of an ionic SOLID is FORMED from its GASEOUS ions under standard conditions .
GAS–> SOLID

Question 2

whats two factors affect lattice energy ?
explain ?
6
1)attratction /energy

Answer 2

• ionic charge :higher charge = stronger electrostatic attraction between ions meaning there will be more energy released when lattice forms
  -size: smaller ions = higher charge density = ions can sit closer together = stronger electrostatic forces .
  the smaller the ionic radius the more exothermic the reaction= more energy released when lattice forms.

Question 3

what happens when you FORM a bond ?

Answer 3

energy released = exothermic

Question 4

what happens when you BREAK a bond ?

Answer 4

energy taken in =endothermic

Question 5

What can Born Harber Cycles calculate ?

Answer 5

lattice Energies

Question 6

How can you calculate the lattice energies ?

- 2 methods

Answer 6

• experimental way (harber cycle )

- theoretical way ( given )

Question 7

How can you tell “ how ionic ,” an ionic lattice is ?

Answer 7

• the difference in the lattice energies( theo and expermental )
• if the difference is small then it’s purley ionic .
• if the difference is large then it has covalent character

Question 8

What the charge density ?

Answer 8

• charge / volume

Question 9

what is the atomisation enthalpy ? (2)

Answer 9

• energy required to produce one mole of free gaseous atoms of that atom .

Question 10

What’s the bond dissociation enthalpy ?2

Answer 10

-enthalpy change when covalent bond is broken homolytically

Question 11

whats the first ionisation energy ? 3

Answer 11

• energy required to remove one electron from each atom -from a mole of free gaseous atoms of that element
• under standard states and conditions

Question 12

What’s the first electron affinity ?2

Answer 12

• energy change when an electron is added

- to each of a mole of free gaseous atoms of that element .

Question 13

whats the atomisation enthalpy of Na? 2

state symbols

Answer 13

Na(s)–> Na (g)

Question 14

first ionisation enthalpy of Na ?2

state symbols

Answer 14

Na (g)–> Na+(g) + e-

Question 15

what the first electron affinity for Cl ?2

state symbols

Answer 15

• Cl(g) + e- –>Cl-(g)

Question 16

the lattice enthalpy can have two meanings ?

2

Answer 16

1) lattice enthalpy of formation

2) lattice enthalpy of dissociation

Question 17

why is the Lattice enthalpy of formation always negative ?

3

Answer 17

• negative = EXOTHERMIC
• this means that bonds are being formed
• which releases energy

Question 18

why is the lattice enthalpy of dissociation positive ?

3

Answer 18

-it is ENDOTHERMIC
- this means that bonds a being broken
- Breaking something requires an input of energy
hence why it absorbs energy .

Question 19

why is atomisation energy always endothermic?

2

Answer 19

• requires energy INPUT to go from solid to gas
• bonds need to be broken
• positive value (+)

Question 20

Why are ionisation ethalpies always positive ?

2

Answer 20

• ENDOTHERMIC

- removing an electron requires an INPUT of energy

Question 21

Why are second ionisation enthalpies more endothermic than the first ionisation energies ?
4

Answer 21

• the energy input required is higher
• this is because the remaining electrons have less repulsion towards one another
• meaning they are more attracted to one another , harder to remove
• HENCE more ENDOTHERMIC ( more input required )

Question 22

why are first electron affinities exothermic ?1

Answer 22

• adding an electron releases energy ( hence exothermic )

Question 23

why is second electron affinity endothermic ?5

NOT FINSHED

Answer 23

• so when you add one electrons (1st electrons affinity) : the charge becomes negative .
• So when you add the second electron , the incoming electron is repelled by over all negative charge .
• its endothermic becauseeeeeee…..

Question 24

how can we tell if a reaction is spontaneous ?

Answer 24

• it is exothermic

Question 25

whats the hydration enthalpy ?

2

Answer 25

energy released when a gaseous ion dissolves in water .

M^x+-(g)->M^x+ (aq)

Question 26

whats the enthalpy of solution ?2

- what happens if it’s exothermic .?

Answer 26

• enthalpy change when one mole of ionic compound dissolve in excess water
• the more exothermic the enthalpy of solution is , the more likely the compound is to dissolve .

Question 27

what’s the hydration enthalpy dependant on ?

2 factors ?

Answer 27

1) size of ion = small charge = High hydration enthalpy

2) charge on ion =Greater charge = stronger attraction to water molecules = High hydration enthalpy .

Question 28

when an exothermic reaction occurs ? what happens to potential energy ?

Answer 28

• potential energy is lowered so that substances become more stable .

Question 29

whats entropy ?1

Answer 29

• the measure of disorder in a system ?

Question 30

Why does a high degree of disorder make something more stable ?

Answer 30

• gases have high entropy : but they are also more spread out ; hence energy is more spread out .
  = more stable .

Question 31

state the states in increasing levels of entropy

Answer 31

solid = lowest entropy
liquid
gas = most entropy