Thermodynamics

Question 1

Define the standard enthalpy of formation Hf

Answer 1

enthalpy change when one mole of a compound is formed from its elements under standard conditions, all R+P in standard states
Na(s) + 1/2Cl2(g) -> NaCl(s)

Question 2

Define ionisisation enthalpy 1stHi

Answer 2

the standard enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to give one mole of gaseous ions each with a single positive charge
Ca(g) -> Ca+(g) + e

Question 3

Define the standard enthalpy of atomisation Hat

Answer 3

enthalpy change when one mole of gaseous atoms are formed from an element in its standard state
1/2Br2 -> Br

Question 4

Define mean bond enthalpy Hbe

Answer 4

enthalpy change when one mole of gaseous molecules each break a covalent bond to form two free radicals averaged over a range of compounds
Br2(l) -> 2Br(g)

Question 5

Define first electron affinity 1stHea

Answer 5

standard enthalpy change when one mole of gaseous atoms is converted into a mole of gaseous ions each with a single negative charge under standard conditions
O(g) + e- -> O-(g)

Question 6

Define lattice formation enthalpy Hlf

Answer 6

standard enthalpy change when one mole of solid ionic compound is formed from its gaseous ions
Mg2+(g) + 2Br-(g) -> MgBr2(s)

Question 7

Define lattice dissociation enthalpy Hld

Answer 7

standard enthalpy chnage hwne one mole of solid ionic compound dissociates into a gaseous ions.
MgBr2(s) -> Mg2+ + 2Br-

Question 8

Define standard enthalpy of hydrogenation Hhyd

Answer 8

standard enthalpy change when one mole of gaseous ions is converted into one mole of aqueous ions
Cl-(g) + aq -> Cl-(aq)

Question 9

define standard enthalpy of solution Hsol

Answer 9

enthalpy change when one mole of solute dissolves to form aqueous ions
NaCl(s) + aq -> Na+(aq) + Cl- (aq)

Question 10

Name 2 factors that increase the strength of an ionic bond

Answer 10

1) Size of ion - smaller ions = stronger attraction
2) charge of ion - higher charged = stronger attraction

Question 11

what do stronger ionic lattices have

Answer 11

1) more exothermic lattice formation enthalpy
2) more endothermic lattice dissociation enthalpy

Question 12

Draw a born-harbour cycle of MgCl2

Question 13

Describe the theoretical Model

Answer 13

name - perfect ionic model
type of ions - point charges, perfect spheres
Nature of bonding - perfectly ionic

Question 14

Describe the experimental model

Answer 14

name - born-harbour
type of ions - polarisable ions
Nature of bonding - ionic+covalent
(more likely to be more exothermic)

Question 15

Define feasible

Answer 15

• the reaction can happen at any given temperature
• feasible when /\G less than or equal 0

Question 16

define entropy

Answer 16

measure of amount of disorder in a system

Question 17

formula for change in entropy

Answer 17

/\S= SumProduct - SumReactant