Thermodynamics

Question 1

Define standard enthalpy of formation

Answer 1

The enthalpy change when one mole of a compound is formed from its elements under standard conditions with all reactants and produce in standard states

Question 2

Define standard enthalpy of combustion

Answer 2

The enthalpy change one one mole of compound is completely burned in oxygen under standard conditions with all reactants and products in their standard states

Question 3

Define mean bond enthalpy

Answer 3

The enthalpy change when one mole of gaseous molecules each break a covalent bond to from two free radicals, averaged over a range of compounds

Question 4

Define first ionisation enthalpy

Answer 4

The standard enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to give one mole of gaseous ions each with a single positive charge

Question 5

Define second ionisation enthalpy

Answer 5

The standard enthalpy change when one mole of electrons is removed from one mole of gaseous +1 ions to give one mole of gaseous ions each with a +2 charge

Question 6

Define standard enthalpy of atomisation

Answer 6

The enthalpy change when one mole of gaseous atoms if formed from an element in its standard state

Question 7

Define first electron affinity

Answer 7

The standard enthalpy change when one mole of electrons is added to a mole of gaseous atoms to form a mole of gaseous ions with a 1- charge

Question 8

Define second electron affinity

Answer 8

The standard enthalpy change when one mole of electrons is added to a mole of gaseous ions each with single negative charge to form a mole of gaseous ions with a 2- charge

Question 9

What is the relationship between enthalpy of atomisation and bond enthalpy.

Answer 9

enthalpy of atomisation is double bond enthalpy

Question 10

Define lattice formation enthalpy

Answer 10

The standard enthalpy change when one mole of solid ionic compound is formed from its gaseous ions

Question 11

Define lattice dissociation enthalpy

Answer 11

The standard enthalpy change when one mole of solid ionic compound dissociates into its gaseous ions

Question 12

What type of reaction is lattice enthalpy of dissociation?

Answer 12

Endothermic

Question 13

What type of reaction is lattice enthalpy of formation?

Answer 13

Exothermic

Question 14

What are the three factors affecting the strength of ionic bonding?

Answer 14

• Charge of ions
• Radius of ions
• Attraction between ions

Question 15

What is covalent character?

Answer 15

Positive ion polarises the negative ion by attracting some of its electron density

Question 16

What is the perfect ionic model?

Answer 16

Ions are perfect spheres, as point charges. Ions can’t be polarised.

Question 17

Define standard enthalpy of solution

Answer 17

The standard enthalpy change when one mole of solid ionic compound dissolves to form its aqueous ions

Question 18

Define standard enthalpy of hydration

Answer 18

The standard enthalpy change when one mole of gaseous ions is converted into one mole of aqueous ions

Question 19

Show standard enthalpy of formation for NaCl.

Answer 19

Na(s) + 1/2Cl2(g) -> NaCl(s)

Question 20

Show first ionisation of Ca

Answer 20

Ca(g) -> Ca+(g) + e-

Question 21

Show standard enthalpy of atomisation for Br.

Answer 21

1/2Br2(l) -> Br(g)

Question 22

Show mean bond enthalpy for Br.

Answer 22

Br2(l) -> 2Br(g)

Question 23

Show lattice formation enthalpy for MgBr2

Answer 23

Mg2+(g) + 2Br-(g) -> MgBr2(s)

Question 23

Show first electron affinity of O

Answer 23

O(g) + e- -> O-(g)

Question 24

Show lattice dissociation enthalpy for MgBr2

Answer 24

MgBr2(s) -> Mg2+(g) + 2Br- (g)

Question 25

Show standard enthalpy of hydration for Cl

Answer 25

Cl-(g) -> Cl-(aq)

Question 25

Show standard enthalpy of solution for NaCl

Answer 25

NaCl(s) -> Na+(aq) + Cl-(aq)