Thermodynamics

Question 1

Define enthalpy of formation

Answer 1

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

EXO

Question 2

Define enthalpy of atomisation

Answer 2

enthalpy change when 1 mol of gaseous atoms are formed from an element in its standard states

ENDO

Question 3

Define enthalpy of 1st ionisation energy

Answer 3

enthalpy change when 1 mol of gaseous ions is formed from 1 mol of gaseous atoms

ENDO

Question 4

Define enthalpy of 2nd ionisation energy

Answer 4

enthalpy change when 1mol of gaseous 2+ ions are formed from 1mol of gaseous 1+ atoms

ENDO

Question 5

Enthalpy of 1st electron affinity

Answer 5

enthalpy change when 1 mol of gaseous 1- ions formed from 1 mol of gaseous atoms

EXO

Question 6

Enthalpy of 2nd electron affinity

Answer 6

enthalpy changed when 1 mol gaseous 2- ions are formed from 1 mol of gaseous 1- ions

ENDO

Question 7

Enthalpy of lattice formation

Answer 7

enthalpy change when 1 mol of solid ionic compound is formed from its gaseous ions

EXO

Question 8

enthalpy of hydration

Answer 8

enthalpy change when 1 mol of aqueous ions are formed from 1 mol of gaseous ions.

EXO

Question 9

Enthalpy of solution

Answer 9

enthalpy change when 1 mol of solute is dissolved in enough solvent that no further enthalpy change occurs in further dilution

ENDO,EXO

Question 10

enthalpy of lattice dissociation

Answer 10

enthalpy change when 1 mol of ionic compound separates into its gaseous ions

ENDO

Question 11

when do you add a 2nd electron affinity(ea) or 2nd ionisation enthalpy(ie) to your born-haber cycle

Answer 11

if there is a 2- ion a 2nd ea is needed

if there is a 2+ ion a 2nd ie

Question 12

When will a reaction be feasible in ∆G

Answer 12

if ∆G is negative -reaction feasible

Question 13

Give ∆G equation

Answer 13

∆G = ∆H - T∆S

Question 14

How can you change numbers in equation to make reaction feasible

Answer 14

Increase entropy-> more positive ∆S

Reaction exo –>more negative ∆H

Question 15

Why is enthalpy change of A larger than enthalpy change of B.

Answer 15

has larger radius/more shells
increased shielding
less powerful attraction (of nucleus) for (outer) e- in B

Question 16

What 2 factors affect enthalpy of lattice formation

Answer 16

Ion Size
The larger the ions, the less negative the enthalpies of lattice formation
(i.e. a weaker lattice). As the ions are larger charges further
apart so have a weaker attractive force between them.

Charge of Ion
bigger the charge of the ion, the greater the attraction between the
ions so the stronger the lattice enthalpy (more negative values).