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inorganic sem 2 > lecture 7🅱️ > Flashcards

lecture 7🅱️ Flashcards

1
Q

enthalpy change

A

the amount of heat evolved or absorbed for a reaction

under constant pressure

H

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2
Q

standard enthalpy change refers to what

A

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

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3
Q

standard temp

A

25*C

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4
Q

standard pressure

A

1 bar

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5
Q

standard conc

A

1 mol dm-3

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6
Q

enthalpy change of formation

A

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

at standard conditions

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7
Q

enthalpy of atomisation

A

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

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8
Q

ionisationenthalpy

A

enthalpy needed to remove electron from element

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9
Q

electron affinity

A

enthalpy change when an electron is added to an element

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10
Q

bond dissociation enthalpy

A

enthalpy change when bonds dissociate

eg: Cl2g -> 2Cl g

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11
Q

bde value can also be

A

2 x atomisation enthalpy

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12
Q

lattice enthalpy

A

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

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13
Q
  • lattice enthalpy issss
A

exothermicccc

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

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14
Q

lattice enthalpy +

A

solid to gas

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15
Q

lattice enthalpy -

A

gas to solid

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16
Q

hess cycle steps for NaCl

A
  • 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 - )
17
Q

hess law definition

A

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

18
Q

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

A

hess law cycle : the new thing

enthalpy level diagram: alevel one

19
Q

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)

A

u need to divide the dbe by 2

or multiply bde by 1/2

20
Q

experimental lattice enthalpy

A

use hess cycle or haber born cycle

21
Q

delta H formation =

A

atom + bde + ie + ea - lattice

22
Q

lattice =

A

atom + bde + ie + ea - formatioon

23
Q

lattice is normally

A

solid to gassss
endothermic

24
Q

solid to gas

A

endothermic
+ lattice enthalpy

25
Q

gas to solid

A

exothermic
- lattice enthalpy

26
Q

experimental lattice enthalpies

A

born harber cycle
hess cycle

27
Q

theoretical lattice enthalpy

A

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.
28
Q

madelung constant

A

accounts for repulsive and attractive forces between ions in a solid, A

depends on structure type

29
Q

if we use madelung constant we also need

A

avo constant

6.022 x 10^23

30
Q

what else is wrong

A

ions arent point charges,, their ion charge can overlap

we use born exponent , n. to account for this.

31
Q

n for 2 elements of the same exponent group

A

n = just that singular number

32
Q

n for 2 elements from different exponent groups

A

add both then divide by 2

basically just get an average of the 2.

33
Q

born lande equation

A

gives theoretical lattice enthalpy

34
Q

z+. z-

A

multiply the ion charges

35
Q

what is r

A

interionic distance

distance from nuc to nuc

radius + radius

36
Q

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

A

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

37
Q

what can born lande be used for

A

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.

38
Q

born mayer equation

A

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

39
Q

kapustinskii equation

A

no knowledge of crystal structure needed,, A or r

lattice energy in kj mol-1

must be in pm

inorganic sem 2 (16 decks)

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