3.1.8 Thermodynamics

Question 1

what is enthalpy of formation

Answer 1

the enthalpy change required to form 1 mole of a compound from its constituent elements. where all the products and reactants are in their standard states. All under standard conditions

Question 2

what is enthalpy of atomisation

Answer 2

enthalpy change when one mole of gaseous atoms is formed from the elements in their standard states

Question 3

define bond enthalpy

Answer 3

the enthalpy change when one mole of a covalent bond is broken into two gaseous atoms

Question 4

define ionisation energy

Answer 4

the enthalpy change required to remove one mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous ions

Question 5

define electron affinity

Answer 5

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 6

what is the second electron affinity

Answer 6

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

Question 7

what is the enthalpy of lattice formation

Answer 7

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

Question 8

what is the lattice enthalpy of dissociation

Answer 8

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

Question 9

what is enthalpy of hydration

Answer 9

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

Question 10

define enthalpy of solution

Answer 10

the standard enthalpy change when one mole of ionic solid dissolves in a large amount of water where the dissolved ions are separated well and do not interact with each other

Question 11

what is the purpose of the born harber cycle

Answer 11

its when lattice enthalpy cant be determined directly. so its done indiirectly

Question 12

why is the second electron affinity endothermic

Answer 12

it takes energy to overcome the repulsive force between the negative ion and the electron

Question 13

what does the perfect ionic model state

Answer 13

when the ions are 100% ionic and spherical
and the attractions are purely electrostatic

Question 14

what is the difference between theoretical and Born Harber (experimental) lattice enthalpies

Answer 14

the born harber is the real experimental value
when a compound shows covalent character those enthalpies differ

Question 15

what is the relationship between born harber anf the theoretical values

Answer 15

the more the covalent character the bigger the difference between the values

Question 16

what factors may cause covalent character in ionic substances

Answer 16

• the positive ion is small
• the positive ion has multiple charges
• the negative ion is charrged
• the negative ion has multiple -ve charges