energetics 2 - lattice energy

Question 1

Enthalpy change of formation

Answer 1

The standard enthalpy change of formation of a compound is the energy transferred when 1 mole of the compound is formed from its elements under standard conditions (298K and 100kpa), with all reactants and products being in their standard states

Question 2

Enthalpy of atomisation

Answer 2

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

Question 3

First lonisation enthalpy

Answer 3

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

Question 4

Second lonisation enthalpy

Answer 4

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 5

First Electron Affinity

Answer 5

The first electron affinity is 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

is the first electron affinity endothermic or exothermic?

Answer 6

The first electron affinity is exothermic for atoms that normally form negative ions because the ion is more stable than the atom and there is an attraction between the nucleus and the electron

Question 7

Second Electron Affinity

Answer 7

The second electron affinity is the enthalpy change when one mole of gaseous 1- ions gains one electron per ion to produce gaseous 2- ions

Question 8

is the second electron affinity exothermic or endothermic?

Answer 8

The second electron affinity for oxygen is endothermic because it take energy to overcome the repulsive force between the negative ion and the electron

Question 9

do first Electron affinity values will become more or less exothermic as you go down Group 7 from chlorine to iodine ?
why?

Answer 9

First Electron affinity values will become less exothermic as you go down Group 7 from chlorine to iodine because the atoms get bigger and have more shielding so it becomes less easy to attract electrons to the atom to form the negative ion

Question 10

Enthalpy of lattice formation

Answer 10

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

Question 11

The strength of an enthalpy of lattice formation depends on… (2)

Answer 11

1. The sizes of the ions
2. The charges on the ion

Question 12

how does the size of the ions affect the strength of a enthalpy of lattice formation?

Answer 12

The larger the ions, the less negative the enthalpies of lattice formation (i.e. a weaker lattice). As the ions are larger the charges become further apart and so have a weaker attractive force between them.

Question 13

how do the charges of the ions affect the strength of a enthalpy of lattice formation?

Answer 13

The bigger the charge of the ion, the greater the attraction between the ions so the stronger the lattice enthalpy (more negative values).

Question 14

lattice enthalpies down a group

Answer 14

The lattice enthalpies become less negative down any group. e.g. LiCi, NaCI, KCI, RbCl

Question 15

Theoretical lattice enthalpies assumes a…

Answer 15

perfect ionic model where the ions are 100% ionic and spherical and the attractions are purely electrostatic

Question 16

When the negative ion becomes distorted and more covalent we say it becomes…The metal cation that causes the… is called… if it… the negative ion.

Answer 16

• polarised
• polarisation
• more polarising
• polarises

Question 17

When 100 % ionic the ions are spherical.
The theoretical and the born Haber lattice enthalpies will be….

Answer 17

the same

Question 18

lonic with covalent character, The charge cloud is … The theoretical and the experimental Born Haber lattice enthalpies will…

Answer 18

• distorted
• differ

Question 19

The polarising power of cation increases when…

Answer 19

• the posive ion has a high charge
• the positive ion is small

Question 20

The polarisability of an anion depends on… The bigger the ion the more easily it is…

Answer 20

• its size
• distorted

Question 21

When a compound has some covalent character- it tends towards giant covalent so the lattice is… than if it was 100% ionic. Therefore the born haber value would be… than the theoretical value.

Answer 21

• stronger
• larger

Question 22

Enthalpy of Hydration

Answer 22

Enthalpy change when one mole of gaseous ions become hydrated such that further dilution causes no further heat change

Question 23

Enthalpy of solution

Answer 23

The enthalpy of solution is the standard 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 24

The strength of a enthalpy of lattice formation depends on the following factors…

Answer 24

1. The sizes of the ions
2. The charges on the ion

Question 25

how does the size of an ion affect the strength of a enthalpy of lattice formation?

Answer 25

The larger the ions, the less negative the enthalpies of lattice formation (i.e. a weaker lattice). As the ions are larger the charges become further apart and so have a weaker attractive force between them.

Question 26

how does the charges on an ion affect the strength of a enthalpy of lattice formation?

Answer 26

The bigger the charge of the ion, the greater the attraction between the ions so the stronger the lattice enthalpy (more negative values).

Question 27

When an ionic lattice dissolves in water, what happens?

Answer 27

When an ionic lattice dissolves in water it involves breaking up the bonds in the lattice and forming new bonds between the metal ions and water molecules.

Question 28

are hydration enthalpies endothermic or exothermic and why?

Answer 28

Hydration enthalpies are exothermic as energy is given out as water molecules bond to the metal ions.

Question 29

how does charge density affect the hydration enthalpy?

Answer 29

The higher the charge density the greater the hydration enthalpy (e.g. smaller ions or ions with larger charges) as the ions attract the water molecules more strongly.

Question 30

When a solid dissolves into ions does the entropy increase or decrease?

Answer 30

When a solid dissolves into ions the entropy increases as there is more disorder as solid changes to solution and number of particles increases

Question 31

For salts where AH solution is exothermic the salt will always dissolve at what temperatures?

Answer 31

all temperatures