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QUB Chemistry Level 2 - Physical Chemistry Summary

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Summary based on all lecture notes from CHM2001 Physical Chemistry. Good luck!

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, Advanced Kinetics
First order reaction
R
A Products
.
>



↳ dCAJIdt = -12 .
[AJt ↳ ti : In2/R ,




↳ [AJt =
[A]o exp( -
k t)
, ( T = 1/R ,




L In[A]e =
In[ASo -
1 t .




* Numerous I'v order run processes A could undergo :


*
↳ [k = 12 ,
+ R, + b ,
,




↳ InCAJe :
In[AJo-t/e



Electronically exited states without Q
nr
III S , g*
111 Sk Rog S + hv /where hu'd hrl
(3) & *
Burg S + A


↳ R 1 and kar-
> 10 order rare constants for radiative + non-radiative
decay

* Creave instant cone of [S * ] -


by shining light on it +
suddenly switching off -
S * Will decay and so will luminescence (hull decay a same


rave

* If rare or decay or S* = r then v =
(Rr + kn/S * ] >
-
11 order decay
↳ It = (t = 0 expl (Ry Rur(t) -
+




↳ ↳Ideay)/[k, =
Go + bur




* Wo quencher , Q , half-life of luminescene decay = tie for "" order =
Ih(2)((Ro + Kur)

* Instead lifetime in absence ,
to , + presence ,
I
, orQ used

↳ //(Rg Kurl time raken for luminescence to decrease to 11e (literime longerrhan tine)
+
invensing
:
to =




↳ It =
100 exp)-t/to)



Measuring lifetime of excited state
* If excired stare studied ,
S *, is luminescent -
it is
easy
* Fire pule of light (usually laser) -
that S(unexcived , ground sware version of molecule) will absorb
, palce or duration much less than

*
lifetime of S

* If S* is Clourescent , Craight after Clash ,
be able to monitor fourescence + its decay as Cone of S *, [S ]
*

, decays wh time
,
due

to say radiative and non-radiative decay processes




X
excitation




If
Remission

,Adding a quencher, Q, to system
* Quencher = chemical species which inveracks we excired stare ,
S *. It may simply just deacrivare in/produce new Chem products .


*
(1) S nu
& S

12) &
*
10 s S + hr /where hr'shr)

(3) & *
Burg S + A

*
(4) S + QRa[Q] , S + Q*
↳ Ra[Q] Pseudo I'r order rare constant made up of product of bimolecular Ra
=
, quenching rare constant
, ,
+ quencher cone
↳ Step 4 is pseudo r order process be [Q] is always [S ] *
,
so val .
of [Q] doesn't really change during quenching xn




Stern-Volmer quenching, based on lifetime
* To = / / (br + Burl

T
* = 1/ (rr + Rur + Ra[Q])

* to /t = 1 + Ksr[Q]

↳ Stern-volmer eq .
(based on lifetime) where Ke =
toRa = Stern-Volmer const.




Typical set of decay profiles for different [Q]

↳ (t = (t = 0 exp) (ny -
+ kn + Ra(a](t)

↳ t = // (lf + Kur + Ra[Q])

So It = (t = 0 expl -
+ /i)




* to =
20ns wI[Q] = 0, 0 2 .


,
0 6 and
.
1 4 M
.




↳ In (1 + / (t 0) = = -


(Rf + Rur + Ra[Q]It
↳ In (1 + 11t 0) = = -

t/t

↳ to /t = 1 + Kir[R]



A-regradients (*10x) 0 051 1/to) 0 07 , 0 11 and 8 10x109s
=
.
= . . .



,



* t = 181 =
to) ,
14 3 9 .


,
.
1 and 5ns




* Calculare gradieurs ( = 1/ to) for [Q]
↳ From this you can calculate values ofI

L Then work our for each value vario (to/t) + Construct SU plor of to lt vs [Q)

↳ Then calculate Kev and Ra




↳ Gradient = Ksv



* Ksv = 2 15M"
.
=
toRa and To :
/Ons (10 = 5x107s")

* Ra = 1 08
.
x 108 M + 5

, Absorbance
A For flourescent dye in absence of Q,
* A =
E C .
.
) =
absorbance =
log(10/1/ a ,




(10 + 1nr)[S ]s
*
↳>C (M" Cm + L labs
absorptivity
=
= molar

L C = conc .
(M) * In presence of Q ,
Lis labs (128 Bur Ra[Q])[S * ]
length (cm) +
↳ 1 =
parn
= + as


* labs = 10 -
1



Flourimeter
* LS = light source (usually Xe-arc lamp-bright + emirs in UV + vis regions (
A M((1) = excitation monochromator ,
usually containing diffraction graving
↳ allows
wavelengrn of excitation (xexcir) to be ser when recording emission Spectrum


* S =
sample that flourescene/phosphoresces in all directions

* MC (2) = emission monochromaror (scanned when
recording emission spectrum

* PD =
Phoro derecror usually phoro multiplier lube

↳a
provides signal that is directly proportional to emirved light invensivy ,
(aemission)
,
that comes through emission monochromaror of wavelength ,
plemission




Stern-Volmer quenching, based on luminescence intensity
(18 )
%
A Measure If in absence and presence (16) of quencher , [Q] , using florimeter
* In fourimever , exciring light intensing is constant and absorbed light insensity ,
labs ,
is constant too as come ,
c
,
of S is constant + so


.. is its absorbance
,
A /Beers law)

save (CS) cone [S * ]
* Assume during irradiation
, cready of produced



Wo quencher
*

L labe =
(10 + Durl [S * ] %


=
[S#]os
·
100 Ry [S ]
*
↳ =
S Ro + Rur + Rp[Q]

A WI quencher ,
[Q] [S ]ss *
Ro + Rur

kj[S ]s
*
↳ 10 =




↳ labc = (Rp + Kur + Ra[Q])(S ] *




* 160/1y = 1 + Ks[Q] >
-
Stern-Volmer ea .
based on luminescence light invensity in absence + presence or quencher

↳ Kor =
to RQ
↳ To =
liferime or S* in absence of Q



Recording data for Stern-Volmer plot
* ser xlexcitation) - ro
usually xmax labsorptions of S

* Ser =Semission) to xmax Semission) of S*
-


Usually
* Measure 1 ,
in absence of Qi . e .
10

* Add known level of [Q] ,
measure new

A Add more Q , measure new I
,
etc .

* Plor 10/1 vs [Q] to Obtain Ks

* 10/1 = 1+ Kir[Q]

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