Thermodynamics

Question 1

What is enthalpy change

Answer 1

The amount of heat energy transferred during a reaction, at a constant pressure.

Question 2

Standard enthalpy of formation (ΔHfꝋ)

Answer 2

Enthalpy change when 1 mole of a compound is formed from its elements under standard conditions

Question 3

Standard enthalpy of combustion (ΔHcꝋ)

Answer 3

Enthalpy change when 1 mole of a substance undergoes complete combustion under standard conditions

Question 4

Standard ionisation enthalpy (ΔHiꝋ)

Answer 4

Enthalpy change for converting 1 mole of gaseous atoms to 1 mole of gaseous cations

Question 5

Standard enthalpy of electron affinity (ΔHeaꝋ)

Answer 5

Enthalpy change for converting one mole of gaseous atoms into one mole of gaseous anions

Question 6

Standard enthalpy of atomisation (ΔHatꝋ)

Answer 6

Enthalpy change when 1 mole of gaseous atoms is formed from its element under standard conditions

Question 7

Bond dissociation enthalpy (ΔHdisꝋ)

Answer 7

Enthalpy change when 1 mole of a covalent bond is broken under standard conditions in the gaseous state

Question 8

Standard lattice formation enthalpy (ΔHlꝋ)

Answer 8

Enthalpy change for forming one mole of solid ionic compound from its constituent gaseous ions

Question 9

Standard lattice dissociation enthalpy

Answer 9

Reverse process of lattice formation enthalpy

Question 10

Factors affecting lattice enthalpy

Answer 10

Ionic Radius- as the larger the radius becomes less exothermic as has weaker electrostatic force of attraction.
Ionic Charge- higher ionic charger means more exothermic and increases charge density due to stronger electrostatic forces of attraction.

Question 11

Comparing lattice enthalpies

Answer 11

Difference in theoretical and experimental data as some ionic compound may contain covalent properties

Question 12

Covalent characters

Answer 12

These may occur if the positive charge is small and strong or the negative charge is big and strong

Question 13

Enthalpy of solution

Answer 13

Ionic solid compound dissolves in water the ionic lattice breaks up and the polar water molecules forms hydrogen bonds with positive and negative ions

Question 14

Enthalpy change of solution (ΔHsolꝋ)

Answer 14

Enthalpy change when 1 mole of an ionic substance dissolves in sufficient water to form an infinitely dilute solution

Question 15

Enthalpy change of hydration (ΔHhydꝋ)

Answer 15

Enthalpy change when 1 mole of a specified gaseous ion dissolves in sufficient water to form an infinitely dilute solution