physical - thermodynamics

Question 1

what is the enthalpy of lattice dissociation

Answer 1

-standard enthalpy change when a mole of solid ionic compound dissociates into its gaseous ions

Question 2

what is the enthalpy of lattice formation

Answer 2

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

Question 3

what is the enthalpy of electron affinity

Answer 3

-first electron affintiy is the standard enthalpy change when a mole of gaseous atoms ions each with a single -ve charge
O(g) + e- = O-(g)
-second electron affinity - add on single -ve charge to form ions each with -ve charge
O-(g) + e- = O2-(g)

Question 4

what is the enthalpy of atomisation

Answer 4

enthalpy change which accompanies the formation of one mole of gaseous atoms from the element in its standard states under standard conditions
Mg(s) = Mg(g)

Question 5

what is the enthalpy of ionisation

Answer 5

standard enthalpy change when one mole of gaseous atoms are converted into a mole of gaseous ions each with a single -ve charge
Mg(g) = Mg+(g) + e-

Question 6

what is the enthalpy of solution

Answer 6

standard enthalpy change when one mole of solute dissolves completely in sufficient solvent to form a solution in which the molecules/ions are far enough apart to not interact with each other
NaCl (s) + aq = Na+ (aq) + Cl-(aq)

Question 7

what is enthalpy of hydration

Answer 7

standard enthalpy change when water molecules surrond one mole of gaseous ions

Na+(aq) + aq = Na+(g)

Question 8

what is enthalpy change of formation

Answer 8

enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions, all reactants and products in their standard states

Question 9

what are the two factors thsnt govern the size of lattice enthalpy

Answer 9

-ionic size
-ionic charge

Question 10

what does a large exothermic value indicate in lattice enthalpies

Answer 10

-large electrostatic force of attraction between oppositely charged ions and that the ionic bonds are strong

Question 11

how do small ions pack tg

Answer 11

very closely and attract each other strongly

Question 12

how do large ions pack tg

Answer 12

far apart and attract weaker

Question 13

what happens as the ionic radius increases

Answer 13

attraction bwt ions decrease
lattice enthalpy becomes less -ve/ less exothermic

Question 14

how does ionic charge affect lattice enthalpy

Answer 14

-most -ve lattice enthalpy are those molecules which have small, highly charged ions
-as +ve charge increases it produces a greater attraction bwt +ve and -ve ions
-ionic radius decreases and ions in lattice become closely packed producing more attraction
-become more exothermic

Question 15

what happens when two opposite charges are present in a lattice

Answer 15

attract strongly and a very exothermic reaction will take place

Question 16

what factors affect enthalpy of hydration

Answer 16

-ionic charge
-ionic size

Question 17

how does ionic size affect enthalpy of hydration

Answer 17

-becomes smaller the value of enthalpy becomes more -ve
-hyrdation depends don the ability of an ion to attract a water molecule
-small ions exert more attraction on water molecules and more energy is released

-as ionic radius increases
-enthalpy of hydration becomes less exo

Question 18

how does ionic charge affect enthalpy of hydration

Answer 18

-as charge increases on an ion it has a greater attraction for water molecules and the enthalpy of hydration becomes more -ve
-across period 3 there is a decrease in size as charge increases - get more exo

Question 19

how are lattice enthalpies measured

Answer 19

using a born-haber cycle

Question 20

what is important to remeber for born-haber cycles

Answer 20

-draw separate step for every enthalpy change - eg each molecule gets own step
-second and third electron affinities are endothermic and shown by drawing arrow going up not down
-write numerical values with each step

Question 21

what are the common pathways for born-haber cycle

Answer 21

1 mole of ionic compound on the bottom
then arrow going to the ionic compound = formation
arrow up from formation = atomisation - need to do separate steps for each element
arrow up from atomisation ionisation - again separate steps for each ionisation
then metal ions at top
arrow down from metal ions to show electron affinity of the non-metal
then arrow down from electron affinity to the ionic compound showing lattice formation

Question 22

what is the triangleHformation

Answer 22

sum of all the other triangle H / enthalpy changes