thermodynamics

Question 1

in exothermic reactions are bond broken or made

Answer 1

in exothermic reactions bonds are formed

Question 2

in endothermic reactions are bonds broken or made

Answer 2

in endothermic reactions bond are broken

Question 3

what factor does the size of an enthalpy change depend on

Answer 3

• the strength/energy of a bond or force

(stronger bonds /forces produce a larger enthalpy change

Question 4

define enthalpy change of formation

Answer 4

the enthalpy change when 1 mole of substance is formed from it’s constituent elements in their standard states under standard conditions and pressure

Question 5

write an equation for the enthalpy change of formation for NaCl

Answer 5

Na (s) + 1/2 Cl2 —-> NaCl (s)

Question 6

define enthalpy change of lattice formation

Answer 6

the enthalpy change when one mole of an ionic compound is from from it’s component ions in a gaseous state

Question 7

write an equation for the enthalpy change of lattice formation of NaCl

Answer 7

Na+ + Cl- —-> NaCl (s)

Question 8

what type of energy change is enthalpy change of lattice formation and why?

Answer 8

exothermic
it is forming an electrostatic attraction (ionic bond)

Question 9

what are the 2 factors that affect enthalpy change of lattice formation and explain why they affect it?

Answer 9

charge on ion = higher charge = strong electrostatic forces between ions = more exothermic lattice formation enthalpy

size of ion = smaller ionic radius = stronger electrostatic forces between ions = more exothermic lattice formation enthalpy

Question 10

define enthalpy change of atomisation

Answer 10

the enthalpy change when one mole of gaseous atoms are formed

Question 11

write the equation for the enthalpy change of atomisation of Na

Answer 11

Na (s) —> Na (g)

Question 12

write an equation for the enthalpy change of atomisation of Cl

Answer 12

1/2 Cl2 (g) —-> Cl (g)

Question 13

write an equation for the enthalpy change of atomisation of Br

Answer 13

1/2 Br2 (l) —-> Br (g)

Question 14

write an equation for the enthalpy change of atomisation of S

Answer 14

1/8 S8 (s) —-> S (g)

Question 15

what type of energy change is enthalpy change of atomisation and why

Answer 15

endothermic, as breaking bonds of attraction

Question 16

define 1st ionisation enthalpy

Answer 16

The enthalpy change to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions

Question 17

write an equation for the 1st ionisation enthalpy for Na

Answer 17

Na (g) —-> Na+ (g) + e-

Question 18

what type of energy change is the 1st ionisation enthalpy change

Answer 18

Endothermic, overcoming electrostatic attraction between nucleus and outer electron

Question 19

what factors affect the 1st ionisation energy

Answer 19

• nuclear charge
• electron shielding
• size of ion

Question 20

define bond dissociation enthalpy

Answer 20

the enthalpy change when 1 mole of covalent bonds are gaseous state

Question 21

write an equation for the bond dissociation enthalpy of Cl

Answer 21

Cl2 (g) —-> 2Cl (g)

Question 22

define 1st electron affinity

Answer 22

the enthalpy change to add 1 mole of electrons to 1 mole of gaseous atoms to make 1 mole of gaseous ions with a -1 charge

Question 23

write an equation for the 1st electron affinity of Cl (g)

Answer 23

Cl (g) + e- —–> Cl- (g)

Question 24

what type of energy change is 1st electron affinity

Answer 24

exothermic as an electrostatic attraction between nucleus and electron is being formed

Question 25

what factors affect 1st electron affinity

Answer 25

- nuclear charge - electron shielding - size of atom

Question 26

define 2nd electron affinity

Answer 26

the enthalpy change when you add one mole of electrons to one mole of gaseous ions with a charge -1 to make 1 mole of gaseous ions with a -2 charge

Question 27

write an equation for the second affinity of oxygen

Answer 27

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

Question 28

what type energy change is 2nd electron affinity

Answer 28

endothermic, electron is being added to an already negatively charged ion. Repulsion between ion and electron must be overcome.

Question 29

define enthalpy of solution

Answer 29

the enthalpy change when one mole of an ionic substance is completely dissolved in water to infinite dilution

Question 30

give the equation for enthalpy of solution of MgCl2

Answer 30

MgCl2 (s) ---> Mg2+ (aq) + 2Cl- (aq)

Question 31

define enthalpy of hydration

Answer 31

the enthalpy change when one mole of gaseous ions is diluted to 1 mole of aqueous ions

Question 32

give the equation for the enthalpy of hydration for Mg2+ (aq)

Answer 32

Mg2+ (aq) + (aq) ----> Mg2+ (aq)

Question 33

define lattice dissociation enthalpy

Answer 33

the enthalpy change when one mole of an ionic solid is converted to gaseous ions

Question 34

give the equation for the lattice dissociation enthalpy of MgCl2 (s)

Answer 34

MgCl2 (s) ----> Mg2+ (g) + 2Cl- (g)

Question 35

what is the equation used to calculate the value for enthalpy of solution

Answer 35

enthalpy of solution = enthalpy of lattice dissociation + enthalpy of hydration

Question 36

define enthalpy of hydration

Answer 36

forces between partial charges of delta positive and delta minus on water are attracted to ions

Question 37

is enthalpy of hydration endothermic or exothermic and why

Answer 37

exothermic as a bond is being formed

Question 38

what 2 factors affect hydration enthalpy and explain why

Answer 38

size of ion smaller ion = higher charge density therefore stronger attraction between partial charges on water and ion = more exothermic hydration enthalpy charge of ion greater charge of ion = higher charge density = stronger attraction between partial charges on water and ion = more exothermic hydration enthalpy

Question 39

define lattice dissociation enthalpy

Answer 39

electrostatic forces between postive and negative ions are overcome

Question 40

why is lattice dissociation enthalpy endothermic

Answer 40

you are breaking bonds

Question 41

what 2 factors affect the lattice dissociation enthalpy and explain why

Answer 41

size of ion smaller ion = higher charge density = stronger electrostatic forces between oppositely charged ions = more endothermic lattice dissociation enthalpy greater charge on ion = higher charge density = stronger attraction between oppositely charged ions = more endothermic lattice dissociation enthalpy

Question 42

what chemical property do ionic compounds with very endothermic lattice dissociation enthalpies tend to have and why

Answer 42

ionic compounds with high lattice dissociation enthalpies tend to be insoluble as a lot of energy is needed to break the ionic lattice (electrostatic forces)

Question 43

if enthalpy of solution is exothermic then what happens to solubility when temperature increases

Answer 43

enthalpy of solution is exothermic so solubility decreases as temperature increases

Question 44

if enthalpy of solution is endothermic then what happens to solubility as temperature increases

Answer 44

enthalpy of solution is endothermic so solubility increases as temperature increases