3.1.8 Thermodynamics

Question 1

Standard enthalpy of reaction

Answer 1

Enthalpy change occurring when the amounts shown in the reaction equation react under standard conditions.

Question 2

Standard molar enthalpy of formation

Answer 2

Enthalpy change occurring when 1 mole of a compound is formed from its elements under standard conditions with all substances in their standard states.

Question 3

Standard molar enthalpy of combustion

Answer 3

Enthalpy change occurring when 1 mole of any compound is burned completely in excess oxygen under standard conditions with all substances in their standard states.

Question 4

Mean bond enthalpy

Answer 4

Enthalpy change occurring when 1 mole of a covalent bond measured in the gaseous state is broken, averaged over a range of compounds.

Question 5

Hess’s law

Answer 5

The enthalpy change for a reaction is independent of the route taken.

Question 6

Calculating enthalpy change of a reaction using bond enthalpy data

Answer 6

reactants - products

Question 7

Calculating enthalpy change of a reaction using enthalpy of formation data

Answer 7

products - reactants

Question 8

Calculating enthalpy change of a reaction using enthalpy of combustion data

Answer 8

reactants - products

Question 9

Bond dissociation enthalpy

Answer 9

Enthalpy change occurring when all the bonds of the same type in 1 mole of gaseous molecules are broken to form gaseous atoms.
e.g. Cl2 (g) -> 2Cl (g)

Question 10

Standard molar enthalpy of atomisation of an element

Answer 10

Enthalpy change occurring when 1 mole of gaseous atoms is formed from the element in its standard state.
e.g. K (s) -> K (g)

Question 11

Standard molar enthalpy of atomisation of a compound

Answer 11

Enthalpy change occurring when 1 mole of a compound in its standard state is converted to gaseous atoms.
e.g. NaCl (s) -> Na (g) + Cl (g)

Question 12

First ionisation energy

Answer 12

Enthalpy change occurring when 1 mole of electrons is removed from 1 mole of gaseous atoms to form 1+ gaseous ions.
e.g. Na (g) -> Na+ (g) + e-

Question 13

Second ionisation energy

Answer 13

Enthalpy change occurring when 1 mole of electrons is removed from 1 mole of gaseous 1+ ions to form 2+ ions.
e.g. Na+ (g) -> Na2+ (g) +e-

Question 14

First electron affinity

Answer 14

Enthalpy change occurring when 1 mole of gaseous atoms is converted to 1 mole of gaseous 1- ions.
e.g. O (g) + e- -> O- (g)

Question 15

Second electron affinity

Answer 15

Enthalpy change occurring when 1 mole of gaseous 1- ions is converted to 1 mole of gaseous 2- ions.
e.g. O- (g) + e- -> O2- (g)

Question 16

Lattice formation enthalpy

Answer 16

Enthalpy change occurring when 1 mole of a solid ionic lattice is formed from its gaseous ions.
e.g. Na+ (g) + Cl- (g) -> NaCl (s)

Question 17

Lattice dissociation enthalpy

Answer 17

Enthalpy change occurring when 1 mole of an ionic substance is separated into its gaseous ions.
e.g. NaCl (s) -> Na+ (g) + Cl- (g)

Question 18

Arrow directions in Born-Haber cycles

Answer 18

ENDO up EXO down

Question 19

Perfect ionic model

Answer 19

Assumes that all ions are perfect spheres with purely ionic attractions (no covalent character).

Question 20

Enthalpy of solution

Answer 20

Enthalpy change occurring when 1 mole of an ionic solid dissolves completely to form aqueous ions.

Question 21

Enthalpy of solution (equation)

Answer 21

enthalpy of lattice dissociation + enthalpy of hydration

Question 22

Enthalpy of hydration

Answer 22

Enthalpy change occurring when 1 mole of gaseous ions is surrounded by water molecules.

Question 23

Entropy

Answer 23

Entropy is a quantitative measure of the degree of disorder in a system.

Question 24

Entropy change (equation)

Answer 24

products - reactants

Question 25

Gibbs free energy change

Answer 25

dG = dH- TdS

Question 26

dG has to be what for a reaction to be feasible?

Answer 26

negative