Enthalpy, entropy and free energy

Question 1

Increase ionic charge

Answer 1

1. lattice enthalpy more exothermic
2. more energy required to overcome electrostatic attraction
3. higher melting point
4. higher thermal stability

Question 2

Decreased ionic radius

Answer 2

1. lattice enthalpy becomes more exothermic
2. more energy required to overcome electrostatic attraction
3. higher melting point
   4.higher thermal stability

Question 3

polarisation

Answer 3

distortion of electron cloud in molecule/ion by nearby positive charge

Question 4

Born-haber cycle

Answer 4

enthalpy change of formation= atomisation metal + ionisation energy metal + atomisation gas + electron affinity + lattice enthalpy

Question 5

Enthalpy change of atomisation

Answer 5

m(s) -> m(g)
1/2x2(g) -> x(g)

enthalpy change when 1 mol of gaseous atoms is formed from the element in its standard state

Question 6

Ionisation energy

Answer 6

m(g) -> m+(g) + e-

enthalpy change to remove 1 electron from each atom in 1 mol of gaseous atoms to form 1 mol of gaseous 1+ ions

Question 7

Electron affinity

Answer 7

X(g) + e- -> X-(g)

The enthalpy change accompanying the gain of 1 mol of electrons by 1 mol of gaseous atoms

Question 8

Enthalpy change of formation

Answer 8

M(s) + X2(g) -> MX2(s)

Enthalpy change when when 1 mol of a compound is formed from its constituent elements in their standard state

Question 9

Lattice enthalpy

Answer 9

aM^b+(g) + bX^a-(g) -> MaXb(s)

enthalpy change when 1 mol of ionic lattice is formed from its constituent gaseous ions
298k and 10KPa

Question 10

Enthalpy change of hydration

Answer 10

enthalpy change when 1 mol of gaseous ions is completely hydrated by water

X^a+(g) -> X^n+(aq)

Question 11

Larger hydration enthalpy

Answer 11

1. smaller ionic radius
2. larger ionic charge
3. increased electrostatic attraction to water molecules

Question 12

Enthalpy change of solution

Answer 12

compound(s) -> X+(aq) + M-(aq)

enthalpy change when 1mol of ionic solid dissolves in water

Question 13

Born-haber cycle hydration

Answer 13

enthalpy of hydration = lattice enthalpy + enthalpy of solution

Question 14

Entropy

Answer 14

measure of dispersal energy in a system
ΔS
KJmol^-1s^-1

Question 15

Increase in entropy

Answer 15

1. solid becomes liquid
2. liquid becomes gas
3. temperature rises
4. solid dissolves in liquid to form a solution
5. products have more molecules in same state

Question 16

Solid entropy

Answer 16

1. low
2. small degree of freedom
3. stuck vibrating particles

Question 17

Liquid entropy

Answer 17

1. greater degree of freedom of movement than solid
2. disperse more energy

Question 18

Gas entropy

Answer 18

1. greatest degree of freedom of movement
2. disperse the most energy

Question 19

ΔS formula

Answer 19

entropy of products - entropy of reactants
KJmol^-1K^-1

Question 20

ΔS total

Answer 20

ΔS system + ΔS surroundings

Question 21

ΔG

Answer 21

ΔH -TΔS

units KJmol^-1

Question 22

Feasibility of reaction

Answer 22

Δ<0

Question 23

Feasibility at equilibirum

Answer 23

ΔG=0

0=ΔH - TΔS
T = ΔH/ΔS

Question 24

0°C

Answer 24

273K

Question 25

enthalpy change

Answer 25

ΔH = enthalpy products - enthalpy reactants

Question 26

Exothermic
Draw profile

Answer 26

ΔH is negative
released energy to the surroundings

Question 27

Endothermic
Draw profile

Answer 27

ΔH is positive
energy is taken in from the surroundings

Question 28

Enthalpy change of formation

Answer 28

enthalpy change when 1 mol of compound is formed from its elements in their standard state under standard conditions

Question 29

Enthalpy change of combustion

Answer 29

enthalpy change when 1 mol of substances is burned completely in oxygen under standard conditions

Question 30

Enthalpy change of neutralisation

Answer 30

enthalpy change an acid and alkali react together completely to produce 1 mol of water

Question 31

SHC of water

Answer 31

4.18

Question 32

negative H
positive S

Answer 32

feasible

Question 33

negative H
negative S

Answer 33

feasible at low temperatures

Question 34

positive H
negative S

Answer 34

never feasible

Question 35

positive H
positive S

Answer 35

feasible at high temperatures