Thermodynamic

Question 1

what is enthalpy change

Answer 1

heat change at constant pressure

Question 2

what reaction is the first ionisation energy

Answer 2

endothermic

Question 3

first electron affinity

Answer 3

energy change when 1 mole of gaseous atoms gain an electron to form 1 mole of gaseous 1- ions

N (g) + e- -> N-(g)

Question 4

what reaction is the first electron affinity

Answer 4

exothermic

Question 5

second electron affinity

Answer 5

energy change when 1 mole of gaseous 1- ions gain an electron to form 1 mole of gaseous 2- ions

V- (g) + e- -> V2- (g)

Question 6

what reaction is the second electron affinity

Answer 6

endothermic

Question 7

enthalpy of atomisation

Answer 7

enthalpy change when 1 mole of gaseous atoms are formed from an element in its standard state

Na(s) -> Na(g)
1/2 F2(g) -> F (g)

Question 8

what reaction is the enthalpy of atomisation

Answer 8

endothermic

Question 9

lattice enthalpy

Answer 9

enthalpy change when 1 mole of an ionic compound is formed from its constituent gaseous ions

Na+(g) + CL-(g) -> NaCl (s)
Zn2+(g) + 2Br-(g) -> ZnBr2

Question 10

what reaction is the lattice enthalpy

Answer 10

exothermic

Question 11

lattice dissociation enthalpy

Answer 11

enthalpy change when 1 mole of an ionic compound is broken into its constituent gaseous ions

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

Question 12

what reaction is the lattice disassociation enthalpy

Answer 12

endothermic

Question 13

bond dissociation enthalpy

Answer 13

enthalpy change when 1 mole of covalent bonds is broken in the gaseous state

Cl2 (g) -> 2Cl (g)

Question 14

what reaction is the bond dissociation enthalpy

Answer 14

endothermic

Question 15

what does the perfect ionic model assume:

Answer 15

• bonding is 100% ionic
• ions exist as perfectly spherical point charges

Question 16

what does the value for lattice enthalpy on the born-haber cycle not match

Answer 16

the perfect ionic model

Question 17

perfect ionic model
Al2O3

Answer 17

Al3+ is a highly charged small ion that is able to distort the electron density of the O2- ion toward itself

Al2O3 has a degree of covalent character

Question 18

how to cause a greater covalent character

Answer 18

• a highly charged small cation
• a large negatively charged anion

Question 19

what does the difference between born haber cycle and the perfect ionic model mean

Answer 19

if they differ significantly, there is a larger degree of covalent character

Question 20

to increase electrostatic attraction:

Answer 20

• higher the charge of +ve and -ve
• the smaller the ionic radii

Question 21

enthalpy of solution

Answer 21

enthalpy change when 1 mole of an ionic compound is dissolved in water

Question 22

what reaction is the enthalpy of solution

Answer 22

can be endothermic or exothermic

Question 23

enthalpy of hydration

Answer 23

enthalpy change when 1 mole of gaseous ions are dissolved in water

Question 24

what reaction is the enthalpy of hydration

Answer 24

exothermic

Question 25

what is entropy (s)

Answer 25

measure of disorder within a system or substance JK-1mol-1

Question 26

what is the entropy at 0 kelvins

Answer 26

entropy is also 0

Question 27

order of entropy

Answer 27

solid - lowest liquid gas - highest

Question 28

what features does a high entropy have

Answer 28

- large Mr/ molecules - higher temperature - liquid -> gas causes an increase

Question 29

how to work out the change in entropy

Answer 29

change in entropy of products - change in entropy of reactants

Question 30

what is Gibbs energy

Answer 30

gives us a way of linking enthalpy and entropy changes during a reaction. tells us about the feasibility of a reaction

Question 31

gibbs energy formula

Answer 31

change in Gibbs = change in enthalpy - kelvin x entropy change G = H - TS convert entropy into kJmol-1

Question 32

how can a reaction to be feasible

Answer 32

change in gibbs must be equal to or less than 0

Question 33

formula to see when a reaction is feasible

Answer 33

T = change in enthalpy / change in entropy

Question 34

change in entropy - +ve change in enthalpy - -ve

Answer 34

-ve = feasible

Question 35

change in entropy -ve change in enthalpy +ve

Answer 35

+ve = not feasible

Question 36

change in entropy -ve change in enthalpy -ve

Answer 36

only feasible at low temperatures

Question 37

change in entropy +ve change in enthalpy +ve

Answer 37

only feasible at high temperatures

Question 38

why does water melt

Answer 38

melts at 0 degrees/ 273k . this is because the value of delta G for the change is 0

Question 39

what is a spontaneous reaction

Answer 39

has sufficiently low activation energy to take place immediately +ve entropy value

Question 40

what is a feasible reaction

Answer 40

has a high activation energy, so must be supplied for the reaction to start

Question 41

when does covalent character occur

Answer 41

covalent character occurs in ions when two joined ions have different sizes/charged meaning the distribution of the charge in not even

Question 42

how to work out lattice enthalpy

Answer 42

LE = hyd - sol