Enthalpy/Born-Haber Cycles

Question 1

Definition of Enthalpy of formation?

Answer 1

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

Question 2

Definition of first ionisation enthalpy?

Answer 2

The energy required to remove 1 electron from each atom in one mole of gaseous atoms of an element to form 1 mole of gaseous 1+ ions

Question 3

Definition of first electron affinity?

Answer 3

The enthalpy change when 1 mole of gaseous atoms gain 1 electron per atom to form 1 mole of gaseous 1- ions

Question 4

Definition of second electron affinity?

Answer 4

The enthalpy change when 1 mole of gaseous 1- ions gain 1 electron per atom to form 1 mole of gaseous 2- ions

Question 5

Definition of enthalpy of atomisation?

Answer 5

Enthalpy change when 1 mole of gaseous atoms are produced from an element in it’s standard state

Question 6

Definition of lattice enthalpy of formation?

Answer 6

The enthalpy change that accompanies the formation of one mole of an ionic compound from it’s gaseous ions under standard conditions

Question 7

Definition of second ionisation enthalpy?

Answer 7

The energy required to remove 1 electron from each atom in one mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions

Question 8

Which enthalpy changes are exothermic?

Go down in born haber cycles

Answer 8

(Formation)
First electron affinity
Lattice enthalpy

Question 9

Which enthalpy changes are endothermic?

go up in born haber cycles

Answer 9

(Formation (rarely))
Ionisation enthalpy
Second electron affinity
Atomisation

Question 10

Why is the second electron affinity endothermic?

Answer 10

1- ion repels electron so energy is needed to overcome the repulsion

Question 11

How can formation be both endothermic and exothermic?

Answer 11

Break metallic/covalent bonds and make ionic bonds - don’t know which is bigger unless you work it out

Question 12

What 5 things do you talk about when comparing lattice enthalpy?

Answer 12

Smaller ionic radius
Larger ionic charge
Greater charge density
Stronger electrostatic force of attraction
More energy released, more exothermic LE

Question 13

Definition of hydration enthalpy?

Answer 13

The enthalpy change when 1 mole of isolated gaseous ions are dissolved in water forming 1 mole of aqueous ions under standard conditions

Question 14

Definition of enthalpy of solution?

Answer 14

The enthalpy change when 1 mole of a compound is dissolved completely in water to form 1 mole of aqueous ions under standard conditions

Question 15

Is hydration enthalpy exo or endothermic?

Answer 15

Exothermic (ion-dipole attraction formed)

Question 16

Is enthalpy of solution exo or endothermic?

Answer 16

Can be both!

Question 17

What 5 things do you use to compare hydration enthalpies of positive ions?

Answer 17

Smaller ionic radius
Larger ionic charge
Larger change density
Stronger attraction on the delta negative O in water
So hydration enthalpy is more exothermic

Question 18

What 5 things do you use to compare hydration enthalpies of negative ions?

Answer 18

Smaller ionic radius
Larger ionic charge
Larger change density
Stronger attraction on the delta positive H in water
So hydration enthalpy is more exothermic

Question 19

What is the equations for enthalpy of formation?

Answer 19

Formation=everything else

Question 20

What is the equation linking Solution, hydration and lattice enthalpy together?

Answer 20

LE + S = Sum of the hydrations

Question 21

How do you work out whether LE or hydration has the bigger effect?

Answer 21

Increase charge density = Increase Solubility = Hydration has the bigger effect
Increase charge density = Decrease solubility = LE has the bigger effect