11 Thermodynamics

Question 1

Define Lattice enthalpy

Answer 1

The enthalpy change when one mole of an ionic compound is separated into its component gaseous ions. (Dissociation)

Enthalpy when one mole of an ionic compounds is formed from its constituent gaseous ions. (formation)

Question 2

Define enthalpy of formation

Answer 2

The enthalpy change when one mole of a compound is formed from its constituent elements, when all products and reactants are in their standard states under standard conditions.

Question 3

Define ionisation enthalpy

Answer 3

The enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to form one mole of gaseous 1+ ions.

Question 4

Define enthalpy of atomisation

Answer 4

The enthalpy change for the formation of 1 mole of gaseous atoms from the element in its standard state under standard conditions.

Question 5

Define mean bond enthalpy

Answer 5

The enthalpy change when one mole of a covalent bond is broken under standard conditions in the gaseous state averaged across multiple compounds.

Question 6

Define electron affinity

Answer 6

The enthalpy change when one mole of gaseous atoms forms one mole of gaseous 1- ions.

Question 7

Define Enthalpy of hydration

Answer 7

The enthalpy change when one mole of gaseous ions is converted to one mole of aqueous ions.

Question 8

Define enthalpy of solution

Answer 8

The enthalpy change when one mole of ions is converted to one mole of aqueous ions.

Question 9

Define perfect ionic model

Answer 9

The ions of an ionic compound are perfectly spherical, with no covalent character.

However, a small cation with a large charge can distort a large anion so that there is covalent character, strengthening the bond.

Question 10

Equation for Gibbs Free Energy

Answer 10

∆G⦵ = ∆H⦵ - T∆S⦵

G and H are kJ mol⁻¹
T is K
S is J K⁻¹mol⁻¹