Unit 1: Section 8- Thermodynamics

Question 1

Define enthalpy change of formation

Answer 1

the energy transferred when 1 mole of
the compound is formed from its elements under standard conditions

Question 2

Define enthalpy of atomisation

Answer 2

enthalpy change when 1 mole of gaseous atoms is formed from the element in its
standard state

Question 3

Define bond dissociation enthalpy

Answer 3

The bond dissociation enthalpy is the standard molar enthalpy change when one mole of a covalent bond is broken into two gaseous
atoms (or free radicals)

Question 4

Define first ionisation enthalpy

Answer 4

the first ionisation enthalpy is the enthalpy change required to remove 1 mole of electrons from 1 mole of gaseous ions with a 1+ charge

Question 5

Define second ionisation enthalpy

Answer 5

The second ionisation enthalpy is the enthalpy change to
remove 1 mole of electrons from one mole of gaseous 1+ ions
to produces one mole of gaseous 2+ ions.

Question 6

Define first electron affinity

Answer 6

the enthalpy change that occurs when 1 mole of gaseous atoms gain 1 mole of electrons to form 1 mole of gaseous ions with a 1- charge

Question 7

Define second electron affinity

Answer 7

the enthalpy change when one mole of gaseous 1- ions one electron per ion to produce gaseous 2- ions

Question 8

Define enthalpy of lattice formation

Answer 8

the standard enthalpy change when 1 mole of ionic crystal lattice is formed from its constituent ions in gaseous form

Question 9

Define enthalpy lattice of dissociation

Answer 9

the standard enthalpy change when 1 mole of an ionic crystal lattice form is separated into its constituent ions in gaseous form

Question 10

Define enthalpy of hydration

Answer 10

the enthalpy change when one mole of gaseous ions become aqueous ions

Question 11

Define enthalpy of solution

Answer 11

the enthalpy change when one mole of an ionic solid dissolves in a large enough amount of water to ensure that the dissolved ions are well separated and do not interact with one another

Question 12

Name the order of the levels in a born-haber cycle

Answer 12

1. enthalpy of formation (pointing downwards)
2. enthalpy of atomisation
3. first and second electron affinity
4. enthalpy of lattice formation
5. enthalpy of lattice dissociation

Question 13

What is the trend in lattice enthalpy as you go down a group?

Answer 13

they become less negative as you go down a group due to the sizes of the ion

Question 14

What is the best size for each ion to be bonded to each other and why?

Answer 14

if ions are a similar size, the ions are able to get closer together, and the attractive forces are stronger. so, a more negative value of lattice enthalpy.

Question 15

What are theoretical lattice enthalpies based upon?

Answer 15

they assume ion clouds are spherical, and so covalent character isn’t accounted for

Question 16

Why are Born-Haber values usually larger than theoretical values?

Answer 16

because covalent character isn’t accounted for in theoretical values, and covalent character usually allows for a stronger lattice to form, and so higher Born-Haber values