lecture 7🅱️

Question 1

enthalpy change

Answer 1

the amount of heat evolved or absorbed for a reaction

under constant pressure

H

Question 2

standard enthalpy change refers to what

Answer 2

enthalpy change when all reactants are in standard states and done in standard conditions

Question 3

standard temp

Answer 3

25*C

Question 4

standard pressure

Answer 4

1 bar

Question 5

standard conc

Answer 5

1 mol dm-3

Question 6

enthalpy change of formation

Answer 6

enthalpy change for a reation where 1 mol of product is formed from its reactants in their standard states

at standard conditions

Question 7

enthalpy of atomisation

Answer 7

enthalpy change that occurs from going from a solid to a gas

Question 8

ionisationenthalpy

Answer 8

enthalpy needed to remove electron from element

Question 9

electron affinity

Answer 9

enthalpy change when an electron is added to an element

Question 10

bond dissociation enthalpy

Answer 10

enthalpy change when bonds dissociate

eg: Cl2g -> 2Cl g

Question 11

bde value can also be

Answer 11

2 x atomisation enthalpy

Question 12

lattice enthalpy

Answer 12

enthalpy change when 1 ol of solid is converted to one mol of gas ions

endothermic (needs energy) to overcome strong electrostatic forces of attraction

Question 13

• lattice enthalpy issss

Answer 13

exothermicccc

refers to the enthalpy of 1 mol of gaseous ions forming 1 mol of solid

Question 14

lattice enthalpy +

Answer 14

solid to gas

Question 15

lattice enthalpy -

Answer 15

gas to solid

Question 16

hess cycle steps for NaCl

Answer 16

• write equation: Na(s) + 1/2Cl2g -> NaCl(s)
• atomisation from S -> G
• bde for Cl2 -> 2Cl
• ionise Na
• electron affinity for Cl
• gas to solid ( lattice enthalpy - )

Question 17

hess law definition

Answer 17

total enthalpy change is independednt of route taken

total enthalpy is the sum of the enthalpy for individual steps

if the states remain the same for pro and rea

Question 18

born haber cycle can be written in 2 ways — its a diagram of individual step reactions

Answer 18

hess law cycle : the new thing

enthalpy level diagram: alevel one

Question 19

bde is going from a diatomic to 2 monatomics so what do we need to do to the dbe value if we only need 1 monatomic (eg: Cl in NaCl)

Answer 19

u need to divide the dbe by 2

or multiply bde by 1/2

Question 20

experimental lattice enthalpy

Answer 20

use hess cycle or haber born cycle

Question 21

delta H formation =

Answer 21

atom + bde + ie + ea - lattice

Question 22

lattice =

Answer 22

atom + bde + ie + ea - formatioon

Question 23

lattice is normally

Answer 23

solid to gassss
endothermic

Question 24

solid to gas

Answer 24

endothermic
+ lattice enthalpy

Question 25

gas to solid

Answer 25

exothermic - lattice enthalpy

Question 26

experimental lattice enthalpies

Answer 26

born harber cycle hess cycle

Question 27

theoretical lattice enthalpy

Answer 27

use of ionic model - ions = hard sphere character - defined ionic radius - ions are sep by internuclear distance 'r' - consider total electrostatic attractions to find lattice energy - difference in potential energy between free ions and ions bound together in solid.

Question 28

madelung constant

Answer 28

accounts for repulsive and attractive forces between ions in a solid, A depends on structure type

Question 29

if we use madelung constant we also need

Answer 29

avo constant 6.022 x 10^23

Question 30

what else is wrong

Answer 30

ions arent point charges,, their ion charge can overlap we use born exponent , n. to account for this.

Question 31

n for 2 elements of the same exponent group

Answer 31

n = just that singular number

Question 32

n for 2 elements from different exponent groups

Answer 32

add both then divide by 2 basically just get an average of the 2.

Question 33

born lande equation

Answer 33

gives theoretical lattice enthalpy

Question 34

z+. z-

Answer 34

multiply the ion charges

Question 35

what is r

Answer 35

interionic distance distance from nuc to nuc radius + radius

Question 36

difference between theoretical (BL) and experimental (HB HC)

Answer 36

BL is based on ionic model,, this is flawed. - no compound is 100% ionic - e- cloud can be polarised if large and negative (low charge) - small and high charge ion (+ ions) can polarise the e- cloud. - this gives higher covalent character

Question 37

what can born lande be used for

Answer 37

assessing how ionic a compound is if theoretical ( BL) and experimental (HB HC) are similar = ionic character big difference = some covalent character present.. describe this quantitatively!! find the %difference.

Question 38

born mayer equation

Answer 38

better born lande one takes ion ion repulsions into account p is constant but in pm,, so interionic distance must also be converted into pm

Question 39

kapustinskii equation

Answer 39

no knowledge of crystal structure needed,, A or r lattice energy in kj mol-1 must be in pm