Chapter 22 Flashcards
What do up and down arrows mean
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
What is definition for LATTICE ENTHALPY
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
What is the standard enthlapy change of formation
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
Why is Latin enthlapy Exothermic
This is because they come together and bonds are made relewidjr energy, so negaive
So how ti sue born Haber cycle step by step
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
Year 12 definitions
Enthakpy change of formation
Isomision energy
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
How to atomisation
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)
Ionsisjtonnenebruoes, remember why is SECOND ionsisjtonnenergy bigger than first,
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
Why is the SECOND ELECTRON AFFINTIY Endothemrif, but first is Exothermic?
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
What to do format wise and with electrons
Format wise lines and then produced on top
For the ionisation energies, add electron there, then these remove when the electron affintiy haooend
Why is atomisation endothermic
A lot of binds broken ti make gas, energy out in, = endothermic
Try make arrows priroitnsl
How is a 3d lattice dissolved with water
How does it look like at the end
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
Standard enthlapy change of so,Troon definition
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 !
How ti find the ENTHAKPY change of soltuion experimentally
EXTRA STEL
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 -
What happens when dissolve 2 step process
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
So how is it done this time, what’s the starting base
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
Why is the enthlapy change hydration always Exothermic
Gas become aqueous so energy released as binds made, negative
What’s the orbkem this time for soltuoj
Just must take care that the soltuoj could be u or down
Okay so what is start and end point for both cycles
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
What’s the effect of increasing RADIUS OF ION , so going down the group, on lattice enthlapy and melting poi “
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
What happens when you go across periods and increase ionic charge
Increases ii ice charge = increased the attraction. Eyeden ions = more nearby produced = more negative enthlay lattice = higher boiling point
Also residue decreases
Remmeber increasing positbe charge across period does nwtabtonrwidus
DECREASES IT AD IT OULLS IN, and this also increases attactjon
Okay so going left right and down
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
Same concept for hydration energy with gaseous atoms?
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
How to try and predict soltubioty with water the basic idea, but why is this not the case always
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
What is a definition of entripy
Entripy is the DISPERSAL IF ENERGY within chemicals making up a chemical system !
What can you think of entripy as
As a measure of chaos and randomness
Therefore, gases will be more chaotic and thus have more entripy
And solids the least
What is the entripy founds t0 k
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
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
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
What’s is the standard entripy if s substance
It’d the entiroh if 1 mole of a substance under standard states and cinruojdnp
Ppp
So 100KPA and 298k
Wnrjopy change?
Is entripy fi procurd - reactants
Always predict the entripy sign and see if matched precaution to doh ke chekc
What does feasibility mean
Whether a rrescrkom can energetically happen
What is Gibbs free energy equation
GIBBS free nee by is the difference of ent Noah + entripy
So = enthlapy - T x entripy
So TEMPERTAURE in Kelvin
For a reaction to be fessbible what’s the condition kout be met
Must be free energy Zless than 0
A decrease in free energy
Remmeber ti convert units
Make sure everything is In KILAJOUKES, MUST DIFIDE ENTRIPY BY A THIUSAND OR IT WOJT WORK
What takes the most importance at room temp vs high temps
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
How to work out change in ENTHAKPY usign standsr cormstion
Pridctd - intial. Always
Until it becomes the autistic bond brwkign thing
How ti find thr MINIMUM TEMO at which reavtion feasible
Use inquelity and set ti 0. At this temp revaruon finally happens and feasible and take dplace
Remember conditions when reaction can be feasible doedns on the signs etc
So make sure if it’s - and entripy - it’s actually ADDING , there are some cases where never fewible
Remmebe ti find formation
Mutlitoky by flipping mow,r wuanrire Blud
R,ember divide thr ENTIROH BY A 1HOUSAND NIT 100
Thus why can endothermic enthlapy changed for dissolving still be fesidbek
Bevause usign entiroh values, gibbed is d it’ll less than 0
Limitations of predictions for feasbukiy
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
So yeah why is that feasible resvriosj don’t happens trisgth away
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
