Chapter 22

Question 1

What do up and down arrows mean

Answer 1

Up arrow means increase in energy. Of energy put IN TO THE SHSTEM (so temp surrounding decrease) = endothermic

Down arrow means decrease , energy being RELEASES into system so Exothermic

More merry put in to break bonds then energy released when bonds broken = endothermic
More energy release downed bonds made then energy rewuired when put in = exothermic

Question 2

What is definition for LATTICE ENTHALPY

Answer 2

Is the the WNTHALPY change that accompanies the formation of ONE mole of ionic compound from its gaseous ions UNDER STANDARD STATES

Can’t calculate this directly so must use born Haber cycle

Question 3

What is the standard enthlapy change of formation

Answer 3

This is the enthlapy change that a commode d the formation of an ionic compound from irs substitute to elements under standard STATES

the end point is the SAME END POINT as when they are gaseous atoms and ions

Both are EXOTHERMIC

Question 4

Why is Latin enthlapy Exothermic

Answer 4

This is because they come together and bonds are made relewidjr energy, so negaive

Question 5

So how ti sue born Haber cycle step by step

Answer 5

There are 2 ROUTES TI GET TWO IONIC COMOUND, and the value of these routes are equal to each other

1) first route is starting with elements in standard states and proper amounts and DIRECLTU GOING TO IONIC COMPOUND BY LATTICE FORMATION
2) second route invokes
- start standar states
- gaseous ions both of them, so atomisation
- then ionisation energy to make one positbe
- then electron affinity to make secon one negative
- now that they are gaseous ions m lattice formation happens to go to ionic lattice

And reranegt to find out answer

Question 6

Year 12 definitions

Enthakpy change of formation

Isomision energy

Answer 6

Enthlapy change of formation is the enthlapy change twoe spalfe when one ole of s compound is formed from its constituent elects under standard states

Ionisation energy is the energy required to remove one electron off one mole of gaseous atoms to form one mole of gaseous 1+ ions

And lattic enethlaly si the enthlapy change accompanied the formation of one mole of iocojc comound from itd Gael du ions undergo standard condtions

Question 7

How to atomisation

Answer 7

Badicsllt if it’d a solid, atomisation makes it a gas

But even if it’d a gas, but in 1/2cl2 (g) form , STILL WILL HAVE TO atomise to make it cl (g)

Question 8

Ionsisjtonnenebruoes, remember why is SECOND ionsisjtonnenergy bigger than first,

Answer 8

Bevause removing one electron off increases relative nuclear charge and so it’s harder to remove an electron off when the nuclear attraction has increased so. Ore energy

Remember this is only when creating +2 ions, if it’d 2 x +1 ions, then just do 2 times

Question 9

Why is the SECOND ELECTRON AFFINTIY Endothemrif, but first is Exothermic?

Answer 9

Initially adding an electron is easy as it makes it stable, so energy is released

But then adding another electorn to an already stable will just cause revulsion, so now ENERGY must be supplied into the system, which causes it to go UP

So down then UP

first electron is attwvtdf to nucleus, so easy to add bind made calm release energy 2nd elevator n repealed from nuckeus o energy neede

Question 10

What to do format wise and with electrons

Answer 10

Format wise lines and then produced on top

For the ionisation energies, add electron there, then these remove when the electron affintiy haooend

Question 11

Why is atomisation endothermic

Answer 11

A lot of binds broken ti make gas, energy out in, = endothermic

Try make arrows priroitnsl

Question 12

How is a 3d lattice dissolved with water

How does it look like at the end

Answer 12

Water has dipoles , so negative attract to positbe ion and positbe hydrogens attwvt to negative ion

Surrounds thr latrice

Ed ti ally the nearby produced by the production of these polar bonds made are enouh to break pre-existing ionic bonds, causing it to dissolve

They END UP SURROUNDIGN THE IONS

Question 13

Standard enthlapy change of so,Troon definition

Answer 13

Enthlapy change that occurs when 1 mol of a solute is dissolved into a solvent

It’s reosetned ad Nacl s + aq —> Na aq + Cl-aq

So overall energy changed required to make one mole solute dissolved
And this can be POSIITVE OR NEGATIVE !

Question 14

How ti find the ENTHAKPY change of soltuion experimentally

EXTRA STEL

Answer 14

Okay so measure mass of your salt

Now start temo of water
Add salt and ther left in, stir until dissolved
Measure maximum TEMPERTAURE reached

Okay now do Q=mC DEKTA T

but as the WHOLE WATER AND SALT changed temp, smss used must be that (assume density if the salt same as water)

Okay now you have mass, find Q
Divide by thousand ti get into Kj
Divide by mikes ti get the Kj per mole

NIW FINAK STEO REMMEBE TI CHEKC JF TEMO ICNREASED , thst mesns energy put so endirhemirf,

So if Theo decreased, it means the salt took energy = Exothermic so +

If temo icnrease, it means alt gave energy = endo Eric so -

Question 15

What happens when dissolve 2 step process

Answer 15

1st steo is thst the ionic lattice breaks, and becomes gaeoudnions again. This is reverse process to lattice enthlapy

Then water surrounds each gaseous atom and makes it AQEUOUS, this is a new energy called HYDRATION ENTHLAY

Question 16

So how is it done this time, what’s the starting base

Answer 16

Starting base = gaseous ions

Okay so first route, hydration to one , hydrauton ti ither, both become aqeuous done

Second route is become lattice first, so lattice enthlapy form gaseous atoms

Then SOKUTION the lattice to become the ions

Question 17

Why is the enthlapy change hydration always Exothermic

Answer 17

Gas become aqueous so energy released as binds made, negative

Question 18

What’s the orbkem this time for soltuoj

Answer 18

Just must take care that the soltuoj could be u or down

Question 19

Okay so what is start and end point for both cycles

Answer 19

For general lattice nehrkay, start is standard states and end is lattice

For soltuoj, start is gaseous atoms, and the end is AQEOUS
One route is lattice enthlapy then soltuoj

Other is just twice hydration

Both routes will equal coming out if thr gaseosu atoms and into the aqueous

Question 20

What’s the effect of increasing RADIUS OF ION , so going down the group, on lattice enthlapy and melting poi “

Answer 20

Increasing radius goes down, decreases the ionic attraction bryweennthenions bevause radius higher

A lower attraction means a WEAKER BOND IS FORMED

A weaker bond produced LESS ENERGY I think of, and LESS ENERBY PRODUCED MEANS LESS EXOTHERMIC WHICH MEANS KESS NEGATIVE

a weaker ionic attraction also means less energy needed to overcome, so melting point decreases

Question 21

What happens when you go across periods and increase ionic charge

Answer 21

Increases ii ice charge = increased the attraction. Eyeden ions = more nearby produced = more negative enthlay lattice = higher boiling point

Also residue decreases

Question 22

Remmeber increasing positbe charge across period does nwtabtonrwidus

Answer 22

DECREASES IT AD IT OULLS IN, and this also increases attactjon

Question 23

Okay so going left right and down

Answer 23

Going fine, residue increases attrvwtuon decrease less energy produced, less negative enthlapy less melting
Going right higher charge less residue tok so more atrcetion better bond more nearby more new grove and more melting

Going left is weird, charge increases, but radius does too so hard to predict

Question 24

Same concept for hydration energy with gaseous atoms?

Answer 24

Here the bind is made between gaseous atom and water

Going down increased radius decreases the attraction thus with water, and thus less energy released and hydration enthlapy less negative

Also going right charge icnrease radius decreases so attrvwtuon with water is stringer more nearby rkeeased si the hydration entkhyo becomes MORE NEAGRUFE

hydration enthlapy always edothemrif bevause always has to water normd kade wmd emehru reels due

Question 25

How to try and predict soltubioty with water the basic idea, but why is this not the case always

Answer 25

Badicsllt we said that if the energy produced when water makes binds Ruth ions exceeds the energy required to break ionic bonds, it will dissolve

Well then, total energy released when water makes binds with ions is HYDRATION ENTHAKPY

And total energy required ti go from gas to lattice is lattice enthlapy, so energy to go from lattice to gas is same thing

Badicsllt if the hydration enthalpy is BIGGER than lattice enthlapy , then therotidlwly the overall change WHICH IS THE SOLUTION should be negative and thus it will disocke

However we see even if the overall change is positive it stil, dissolved smf thid id to do with entropy

Question 26

What is a definition of entripy

Answer 26

Entripy is the DISPERSAL IF ENERGY within chemicals making up a chemical system !

Question 27

What can you think of entripy as

Answer 27

As a measure of chaos and randomness

Therefore, gases will be more chaotic and thus have more entripy

And solids the least

Question 28

What is the entripy founds t0 k

Answer 28

At 0K, nothing had any energy, there is no chaos and no randomness so entripy is 0

But when you move to a higher entripy level, so solid to liquid, entripy INCREASES as more chaotic

Final entity - intial = entripy change and this will be a PSOTIIBE ENTIROH CHABRG

but if you fit firm gas ti liquid entripy goes less, entripy change is NEGATIVIE

Question 29

Okay so you can predict entripy change sign if it’s solids to liquids and gases, but what if iRS ALL GASES in the reaction what hspoens then

Answer 29

Looks at the number of moles

You’ll see if it goes form high kohl’s to less, then the arena net of randomness of osrtickes SECREASES, entiroh decreases so change is negaitve

Question 30

What’s is the standard entripy if s substance

Answer 30

It’d the entiroh if 1 mole of a substance under standard states and cinruojdnp
Ppp

So 100KPA and 298k

Question 31

Wnrjopy change?

Answer 31

Is entripy fi procurd - reactants

Always predict the entripy sign and see if matched precaution to doh ke chekc

Question 32

What does feasibility mean

Answer 32

Whether a rrescrkom can energetically happen

Question 33

What is Gibbs free energy equation

Answer 33

GIBBS free nee by is the difference of ent Noah + entripy

So = enthlapy - T x entripy

So TEMPERTAURE in Kelvin

Question 34

For a reaction to be fessbible what’s the condition kout be met

Answer 34

Must be free energy Zless than 0

A decrease in free energy

Question 35

Remmeber ti convert units

Answer 35

Make sure everything is In KILAJOUKES, MUST DIFIDE ENTRIPY BY A THIUSAND OR IT WOJT WORK

Question 36

What takes the most importance at room temp vs high temps

Answer 36

Normally vlaue of enthlapy much bigger so entripy doesn’t play much if a part

But when eorgwured icnrease, the temo fsctor plays part snd now the entripy dominated the EQUATUIN more

Question 37

How to work out change in ENTHAKPY usign standsr cormstion

Answer 37

Pridctd - intial. Always

Until it becomes the autistic bond brwkign thing

Question 38

How ti find thr MINIMUM TEMO at which reavtion feasible

Answer 38

Use inquelity and set ti 0. At this temp revaruon finally happens and feasible and take dplace

Question 39

Remember conditions when reaction can be feasible doedns on the signs etc

Answer 39

So make sure if it’s - and entripy - it’s actually ADDING , there are some cases where never fewible

Question 40

Remmebe ti find formation

Answer 40

Mutlitoky by flipping mow,r wuanrire Blud

Question 41

R,ember divide thr ENTIROH BY A 1HOUSAND NIT 100

Question 42

Thus why can endothermic enthlapy changed for dissolving still be fesidbek

Answer 42

Bevause usign entiroh values, gibbed is d it’ll less than 0

Question 43

Limitations of predictions for feasbukiy

Answer 43

Doesn’t take into account kinetics if it, like rate if reavtion, activsitonnenegry

Like thud it might be feasible at 25 but never happen because activwitonnenrby so high it the rate if rescruin jd do low

BUT IF LEFT FOR LOMG EMOUGH IT WOULD HAPPEN

Question 44

So yeah why is that feasible resvriosj don’t happens trisgth away

Answer 44

Because rwte if reavtion slow ewcorvon energy high

Can speed up with csltyst

There will be always some molecules the Thisbe enough energy to do the drewciro;tho

And if leave for long enough ti should hapless Logan’s it is feasible