THERMODYNAMICS - PHYSICAL 2

Question 1

What does size of enthalpy change depend on

Answer 1

-strength / energy of bond or force
-stronger the bond, stronger the enthalpy change

Question 2

enthalpy change of formation

Answer 2

enthalpy change when 1 mole of substance if formed from its component elements in their standard states

Question 3

eg of enthalpy change of formation

Answer 3

Na (s) + 1/2Cl2 (g) > NaCl(s)

Question 4

enthalpy change of lattice formation

Answer 4

enthalpy change when 1 mole of ionic compound id formed from its component ions in gaseous state

Question 5

eg of enthalpy change of lattice formation

Answer 5

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

Question 6

type of energy change of enthalpy change of lattice formation and formation

Answer 6

-exothermic
-ionic bonds
-with strong electrostatic forces of attraction being formed

Question 7

Factors affecting strength of enthalpy change of lattice formation

Answer 7

-Charge on ion > greater charge then strong electrostatic force of attraction between ions > more exothermic lattice formation enthalpy

-size of ion > smaller ionic radius > stronger electrostatic forces between ions > more exothermic lattice formation

Question 8

enthalpy change of atomisation

Answer 8

enthalpy change when 1 mole of gaseous atom are formed

Question 9

eg of enthalpy change of formation

Answer 9

Na (s) > Na (g)

1/2Cl(g) >Cl (g)

Question 10

Type of energy change of enthalpy change of atomisation

Answer 10

endothermic > breaking bonds of attraction

Question 11

1st ionisation enthalpy

Answer 11

enthalpy change to remove 1 mole of e- from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions

Question 12

eg of 1st ionisation enthalpy

Answer 12

Na (g) > Na+ (g) + e-

Question 13

type of energy change of 1st ionisation enthalpy

Answer 13

endothermic > overcoming electrostatic forces of attraction between nucleus and outer e-

Question 14

factors that affect strength of 1st ionisation enthalpy

Answer 14

-nuclear charge
-e- sheilding
-size of ion

Question 15

bond dissociation enthalpy

Answer 15

enthalpy change when 1 mole of covalent bonds are broken into gaseous state

Question 16

eg of bond dissociation enthalpy

Answer 16

Cl2 (g) > 2Cl (g)

Question 17

1st e- affinity

Answer 17

enthalpy change to add 1 mole of e- to 1 mole of gaseous atoms to make 1 mole of gaseous ions with 1- charge

Question 18

eg of 1st e- affinity

Answer 18

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

Question 19

type of energy change for 1st e- affinity

Answer 19

exothermic >forming electrostatic forces of attraction between nucleus and an e-

Question 20

factors that affect strength of 1st e- affinity

Answer 20

-nuclear charge
-e- shielding
-size of atom

Question 21

2nd e- affinity

Answer 21

enthalpy change of 1 mole of e- added to 1 mole of gaseous ions with 1- charge to make 1 mole of gaseous ions with 2- charge

Question 22

eg of 2nd e- affinity

Answer 22

O- (g) + e- > O2-(g)

Question 23

type of energy change in 2nd e- affinity

Answer 23

endothermic >repulsion between ion and e-

Question 24

Factors affecting lattice enthalpy

Answer 24

-stronger ionic bonds> stronger electrostatic forces between ions
-ionic charge > highly charged ions form stronger ionic bonds so electrostatic attraction
-ionic radius > smaller ions have greater charge density > form stronger ionic bonds so stronger electrostatic forces

Question 25

perfect ionic model

Answer 25

-perfect spheres
-no covalent interaction

Question 26

ionic compounds with some covalent character

Answer 26

-some ionic compounds have distorted ions that are no longer spheres and some covalent interaction
-e- clouds of ions overlap and form weak covalent bond
-covalent bond stronger than ionic bond and lattice enthalpy will be more exothermic

Question 27

Theoretical lattice enthalpy

Answer 27

-assumes ions as point charges and calculates the energy of attraction between them
-assumes ionic compound has perfect ionic model

Question 28

experimental lattice enthalpy

Answer 28

-calculated using born-haber cycle
-enthalpy changes in cycle have ultimately been found using experiments

Question 29

comparing theoretical and experimental lattice enthalpy if values are very similar

Answer 29

-compound has only ionic bonds and obeys perfect ionic model
-perfect spheres and no covalent character

Question 30

comparing theoretical and experimental lattice enthalpy if experimental value > theoretical value

Answer 30

-actual bonding is stronger (more exothermic)
-compound has some covalent character and ions have been distorted so no longer spheres

Question 31

Why do some ionic compounds have covalent character

Answer 31

if + ion is polarising it pulls e- cloud of the - ion towards itself, distorting ion and creates overlap of clouds creating weak covalent bond

Question 32

factors affecting polarising ability of positive ion

Answer 32

-ionic radius > smaller ions have greater charge density > more polarising
-ionic charge > more highly charged ions have greater charge density > more polarising

Question 33

factors affecting polarising ability of negative ion

Answer 33

-ionic radius > larger ionic are easier to distort
-ionic charge > lower charged ions re easier to distort