00:05
OK her you guys Dillon while 2
00:09
more lectures a review the
00:15
final for the final on
00:16
Friday so all really be doing on Friday but tell you in
00:22
some detail it's going to be honored did I mention that the
00:27
electronic course evaluations are available and look to see if any of you guys did these the
00:34
last 2 days Monday we talked about enzyme kinetics but were not going to say
00:41
anything more about that today but as you'll see on Friday that stuff we're going to be on the final so I J and a lot of information into that lecture on Monday all of enzyme kinetics all of enzyme inhibition it's all in there all right some of that stuff is not in your book like the enzyme inhibition stuff OK so you can either find another source just to study that found where you can study it directly from the lecture I think everything that I put in theirs
01:18
approximately correct now today I wouldn't talk about transition state period at the
01:26
beginning of the quarter this is what we hope the cost would look like we
01:32
had this beautiful blue rectangle of reaction dynamics here at the end of the course it we're optimistic that we'll be able to
01:40
talk a lot about this maybe from more than 1 lecture what
01:45
actually happened it was it fell off the end of the course In all we've got left is a single lecture but you're going to hear about today but that's all
01:57
that's left of reaction dynamics could we have just left it out we could have but enough damage has been done to you guys In 1 31 8 all you heard about was quantum mechanics from Professor Ren In 131 Be all you heard was about was that cost could be from Professor Martin and I know you know a lot about 1 mechanics and spectroscopy and that's good but everything else is important to so this
02:29
subject is actually very very important to us and so I
02:35
tried to pick out the 1 thing that I cannot allow you to leave this class without knowing I've tried to pull the 1 thing odd reaction dynamics that you you got a Nobel right this is the 1 thing this lecture prime mentality basically what we
02:56
want understand is where does the Arrhenius equation come from when we measured the temperature dependence of reactions this is the reaction rate
03:08
most of the time we find out that it
03:11
conforms to this equation right we make a
03:15
plot of a lot of the
03:18
reaction rate versus 1 over tea would get a straight line we get the activation energy the reaction from that straight line we report
03:25
that we think about that that guides a lot of what we do is physical chemists but we have never explained where this equation comes from right in some ways this is the most important equation in chemical kinetics but we haven't talked about what its origin is fundamentally word does this equation comfort so I wouldn't do that to date I can do that in 1 lecture it reminds me
03:57
of course this statement is
03:58
grammatically incorrect it's a
04:03
dangling prepositioned there might 1 my favorite jokes the
04:06
Texans Texas student goes to Harvard in In his asks a Harvard
04:12
student worry from the Harvard registers welcome from place we do not and our senses of propositions the 2nd OK
04:22
where are you from In other words
04:28
the sometimes substitute felt that so I would love to spend 10
04:35
minutes talking to you about these 2 guys Henry area worked at the
04:41
University of Utah for most of his
04:43
career 1 of the great American physical chemist of the 20th century Michael Pliny Nobel Prize-winning
04:52
physical chemist by both of these guys are responsible for ordinary talk about today
04:58
transition state theory
05:00
they work it out in the 1930 so here's the short version of the history that matters here way back
05:09
in 1916 she analysts the 1st
05:12
Great American physical chemist
05:17
Morgan to lose .period structure
05:21
right there was no quantum mechanics and 1916 was invented until 1924 he came up with a very compelling model for chemical bonding involving pairs of electrons that turned out to be correct and all much of what it predicted the way before the fundamental underpinnings of quantum mechanics were described he figured all add
05:45
up he was a genius Heisenberg interact ensuring their discovered quantum mechanics in 1924 but
05:53
Germans Hi learned Fred Heiler
05:58
in London rather took 1
06:03
mechanics applied at the bonding for the 1st time they did the 1st quantitative description of chemical bonding their names are usually last year we hardly even mention sometimes
06:13
we talk about London's dispersion forces remember
06:17
that Vander walls forces that is the guy Fritz London is together figured that out all right
06:25
1929 5 years after quantum mechanics these guys developed a
06:31
quantum-mechanical 1 way to think about reaction rates write these guys
06:37
figured out a quantum-mechanical later to think about bonding that's
06:40
pretty important Michael Pulandian airing figured out how to think about reaction rates quantum-mechanical sp perspective right Oregon
06:49
zoomed froze what they taught us today here's the
06:56
basic idea it was the ghost of products which is going to talk about this generic reaction today where we strip
07:05
down this lecture so that we've taken everything else out it should be 3 weeks worth elections we know
07:12
the radar Is that but the rate constant times the concentration of a cancer concentration of meat these can be pressures or concentrations the transition state theory says that this reaction actually occurs through this mechanism write a plus
07:33
B are in equilibrium with something called a B double and that reacts in the use of molecular fashion editors products all right transition
07:46
state theory basically takes
07:48
all of the reactants but some on 1 side of the products but some on the other side and in between it constructs something
07:57
called and activated complex or transition state that's why it's called transition state theory this thing here is
08:05
the transition state all
08:08
right that's an entity that is
08:12
intermediate between the reactants and the products if Bonds exist in the products that don't forming the reactants they exist partially in a weak form in the activated complex on the transition state if Bonds are welcome here the partially broken In the
08:33
transition state so the transition state has
08:36
structural attributions bond lengths and so on better intermediate
08:41
between the reactants and the products 1 of the key
08:47
points about transition state there is a postulates
08:49
that an equilibrium exists between this transition state enemies reactants Rice so here's the picture in terms of
09:03
energy that you've seen a million times but what were presented here now the notation applies specifically to transition state theory you've got
09:12
reactants that represented here by these 2 molecules this looks like it could be and OH that CH story that's the age 3 b or are apparently right away minors seats 3 art that's the transition state OK and you're the products notice that in this reaction a new bond is formed between this oxygen in this carbon and this bond here between this government and this bromine is broken
09:49
OK on the transition state noticed that the transition state what were depicting here is this bond is partially form you see how long it is it's a long time we
09:59
bond right and that bond
10:03
is partially broken seal along it is it's a long week bond also by that bond is going to be broken in the product state that Bonn doesn't even exist in the reactants states or the
10:15
transition state contains all of the bonds that are present in the reactants and in the products all right but the bonds that are involved in the
10:25
formation of the products from the reactants are weakened
10:30
right see how long that is see along that bond is these are 2 Super weak bonds all right so we can
10:38
construct a transition states by thinking about what the products
10:42
look like what the reactants look-alike products reactants and then thinking about how the products
10:49
are formed from the reactants geometrically how does that happen all right this
10:55
shows an attack in a particular geometrical orientation of the OH minus to the home CH 3 R while thinking about this and thinking about this we can construct what this transition state should look like
11:11
try using a few simple rules now
11:18
transition state and activate complex should not technically be used interchangeably there's a new wants but the the activated
11:27
complex actually exists over range of this reaction coordinate whereas the transition state in principle exists only at a particular point in time
11:36
we're not going to bother ourselves with that distinction today but there's a fine point there but you should know these are not identical we're
11:44
not into interchangeable to say activated complex in transition date but today were
11:49
just an EU source 2 terms interchangeably OK With
11:57
that as a premise let's see if we can work out what the reaction radiates here's
12:03
our mechanisms are transition state theory mechanism for this reaction criticism that his death so we can write an expression for this equilibrium constants but
12:14
what is the product over
12:17
reactants notice that normalizing being very careful here To write
12:23
activities the activities of the transition
12:26
state the activity of a the activity of the chasm dividing by the standard concentration in the air OK and so when we're done canceling the C 0 up the next effective Caesar on the numerator that ensures that the equilibrium constant is
12:43
dimension as all right now unfortunately I use the
12:49
Microsoft Word Equation Editor tried a lot of these equations it does not allow me to write a 0 with a
12:57
line through it all right that is the symbol for the standards concentration 1 molar for
13:08
example but understand called C
13:11
0 right there's another issue see Double X here this double Microsoft Equationator
13:21
editor doesn't contain a dying sets what's the diocese's it's that they're
13:25
saying the double dagger the double dagger is the same thing
13:30
as their dioceses so when I write to pluses unjust indicating the transition state OK so that
13:40
refers to the transition state that's the equilibrium constant that involves the transition state that's the read you the molecular reaction rate constant that involves the transition state you see how I'm a right that is that you see the double plus
13:54
it's just the diagnosis if you can if anybody knows a work-around for that I would that would help me a lot how do I
14:05
write a dioceses and Microsoft equation editor here I cheated at Pope told I put a white square least this on top
14:14
but I thought I can do that is 106 lies in his presentation but now
14:22
suggest the directors in terms of pressures if we want to all right here's concentrations pressures no different now
14:32
if we flash that were talking right now but Chapter 20 if
14:36
we find that the chapter 17 it turns out we can
14:41
calculate equilibrium constants from partition function all right and recall partition functions are
14:48
very important to us because they allow us to make a connection between statistical mechanics thermodynamics partition functions contain information about the actual molecule we can look at a molecule of we know something about its state distribution we can write a partition function all right
15:05
what we learned in Chapter 17 what we didn't
15:07
have time to talk about in the class this quarter is the fact that you can also use these partition functions to calculate
15:14
equilibrium constants if you wanna read more about that it's on page 670 turns out to be a sort of an important thing that we left out here's what's there right here some generic reaction tables the baby balls of Moses leading roles of the here's what the equilibrium constant expression looks like written out in terms of the standard more partition functions for a B C and
15:42
all right so if I know I can
15:44
calculate these partition functions for all of these guys and I know that so what is this is the standard more petition for em smaller areas species a what's that that other guy number that's not a miss print right it's Our Daughters
16:03
number in every single case
16:05
that is the difference in 0 . energies between react in some products so if this is your generic reactant here's your vibrational energy levels here a
16:16
vibrational energy at levels of the products right that's the ground vibrational energy level that's the ground vibrational energy level that's Delta already 0 but the difference between the
16:27
ground the 0 . energies of the reactants in the products
16:34
OK so here's our Gibbs free energy as a function of reaction coordinate all right the delta r e 0 is closely related to this green they are of quantity than indicating here all right if this thing was in but ground vibrational energy level and this thing was its ground vibrational energy level both of these guys and both of these guys then this would be dealt are ye 0 Frank because
17:09
we're always talking about the 0 . energy and we could say
17:14
something about this equilibrium constant we could calculated using this equation right here now in transition state theory
17:20
that's not the equilibrium constant we care about what we say in transition state theory is this is an
17:27
equilibrium with that's why I don't care about the equilibrium of this with various that's going give me the normal equilibrium constant that I can learn about
17:35
Chapter 17 where public transition state theory says it these 2 guys are in
17:41
equilibrium with 1 another so what matters is this Delta already 0 here right this thing that we normally call the activation energy it's
17:50
the activation energy from the Arrhenius equation all right so we
17:55
want a calculated that
17:57
imaginary equilibrium constants right because these things may actually be
18:04
an equilibrium but this thing is not really observable except using some exotic
18:08
spectroscopic nanosecond Akiko 2nd spectroscopy OK
18:15
so it a normal equilibrium applied to this generic reaction right here I could calculate the equilibrium constant using this equation so now apply that same thinking to the transition state theory here's the transition state equilibrium we care about the reacts PD give this transition state and so now what I want I want .period that partition function for that guy in the numerator for these guys in the denominator in and that's of goggles number that's just left over from it's next
18:45
effective of goggles number because of 2 reactants 1 product who so
18:53
I can calculate this equilibrium constant that applies to the
18:58
formation of the transition state all right now keep in mind everything we're talking about here is kinetics right were sort of mixing thermodynamics with kinetics they took a thermodynamic
19:10
concept equilibrium constant and applied that to transition state OK so you with me so far we've got an equilibrium constant here we can calculate using statistical mechanics to estimated OK that's the 1st thing to
19:29
understand but the 2nd thing to understand is that this
19:34
rate right here showing grain that's going to be approximately equal to that of the which with with which the
19:46
transition state classes over the top of the barrier we've got a barrier
19:51
here we've got a transition state this we are moving along this reaction coordinate from reactants to products the frequency with which this thing moves across the top of this barrier that's gonna closely approximated this way but the rate at which products
20:08
are formed but that seems to be a statement of the obvious right obviously as you cross over this barrier for reactants the products the frequency that that happens that's the rate reaction
20:21
and the it's probably obvious to say that McCain so the reaction rate I can write as this frequency times whatever the concentration of this transition
20:33
status White we're going to talk
20:36
about this frequency right if the frequency with which if you think about this as being a molecule all right there's a
20:45
vibration that has to happen here all right this guy
20:49
moves back and forth between these 2 guys I would get a symmetric
20:55
vibration of this transition state the frequency that characterizes that mold is the frequency that we care about now your book
21:07
includes something called the transmission coefficient were dismissed and that's what that Kappa right there just forget about it it's 1 OK so the rate
21:19
of the reaction is given by the special frequency that applies to the reaction coordinate times the concentration of the transition state but we know we can also write the rate in the normal way With the rate constant times they tend to be right it's what we've been saying all
21:36
along so we can but the here was
21:42
art equilibrium constant expression for the transitions transition state unifies just all a this expression right here I get this and I can plug that into a B there right so I just solve the concentration of the transition state from here OK and applied that to this equation right here and of summer put all of this in the here and so there there's the there's the frequency the special frequency hears all the rest of at but that's the reaction rate
22:30
so in essence this is the phenomenal logical rates expression that we would normally right for this reaction
22:37
A-plus goes to products we know that the reaction rate Kate time 8 times Beaver is 1 that's elementary reaction right right and what we said is
22:46
love that would rate constant is given by this expression right here that frequency times that equilibrium constant divided by this concentration term just to keep the unit's writes the transition
23:01
state theory has already and the
23:04
important thing is that these 2 parameters here
23:07
relate directly to physical parameters of the transition state that we can think about calculating In other words we can calculate this way
23:16
constant from fundamental properties of the transition state because we know
23:21
enough physical chemistry to do that already OK so
23:28
here's arches so we have the key point is we have expressions but equilibrium constant and for this rate constant right here we said That's just equal to the this guy's c 0 times Kerry double dagger divided by the OK and so on let's say that
23:54
we actually do want calculate now but the rate constant but said that we actually
24:00
won a calculated that right there we have to be able to calculate became double dagger without being able calculate locator Leger which assisted living How are we going to do
24:11
that well use the expression for
24:13
making a double dagger we know what the partition function of a and B are we know to calculate that a ready we've done that How do we
24:21
calculate the partition function of the trenches transition state had we calculate that
24:27
partition function is don't In the
24:40
that's the same as that that's the same as that 1 way out of it's a little
24:47
confusing isn't it what the heck to search that's also became a
24:56
sorry that should be capable there that's just became a sorry you're right those that double-decker should be there thank you OK How do we calculate that France's state and how we calculate that partition function it's a
25:16
trend transition state for goodness sake but what is it this is the
25:21
question that these guys wrestled with women worked out the transition state theory right if we think about the vibrational trip
25:31
partition function 1st right it's the vibrational partition function that we really care about here right essentially the transition state undergoing a vibrations all right I hardly
25:46
think about that maybe this bond is getting longer this spot is getting shorter all right it's like an
25:56
asymmetric stretch of the transition state that's the mold that we care about so if we could calculate the partition function for that vibrational mode
26:07
that's critical to understanding what the reactionary is going to be right so here's the generic expression for the vibrational partition function right for some
26:17
mode that has a natural frequency or natural energy H New and natural frequency New all right now what can we say about this magic mode that we care about this asymmetric vibration along this axis is that going to be
26:37
high-frequency motor low-frequency known what you guys think High Frequency but you have what and so on tell me this is
27:03
a weak bonds here right do we bonds have
27:09
high frequencies are low frequencies yeah thank you
27:15
parts of organ expect this to be a week I wouldn't expect this to be a very low frequency mode call
27:24
right here is a picture from Europe chapter that I think is somewhat not intuitive all right here's the transition state up here what what this picture is trying to convey is that the transition state as a very shallow vibrational energy well with varied with vibrational
27:45
energy levels are very very close together in energy all right in other words the frequency
27:52
you have to go from here To hear that each new is tiny right yes but
28:06
the key point is that the frequency that characterizes these transitions in the transition state along this direction right here is very small so that allows us to do simplify this equation we can write this exponential as as a series and we can truncated at
28:26
the 1st term and when we do that we just get that
28:30
Katie overreach New fight we take this normal expression for the partition function we truncated we write it as a series expansion the exponential we truncated at the 1st term it would just get Katie overreach knew this is a special new This is the frequency that describes
28:51
motion over the barrier but whatever that is for whatever the transition state is whatever mold the product bonds are getting formed reacted bonds are getting consumed we can think about that processes involving a single vibration that has a very low frequency in general if that's what they realize conceptually this is not obvious I think everybody in this room would agree none of this stuff and talk about last by bandits is obvious but this was the conceptual leap that Maine OK so I can write the
29:29
whole partition function for the transition state as the partition function for this little frequency mode and then the whole rest of the partition function right noticed that there's
29:41
going to be a rotational and electronic translational right the partition function contains many other manifolds and other vibrational modes as well for the molecule that are orthogonal write to this special mode but with a role
29:56
that fall into this guy over here this is just the partition function for
30:01
the Magic mode the corresponds to the reaction this is the rest of
30:06
Q all the rest of the partition function for all the other
30:10
modes manifolds and so on OK so that's the
30:16
petition and I just plugged that in the end here's the partition function that we were wondering about the expression we now have 4 notice that the rest of this partition function
30:28
involves things that we can't already calculated because the things "quotation mark not perturbed in the molecule but what's perturbing the transition state is product bonds are getting formed react bonds are getting broken right and we can describe that we can roll that process all
30:46
into up into 1 Mauldin has this characteristic frequency here we're going to have to figure out
30:51
what that frequency it all right but
30:54
all the rest of the stuff we could is rolling in right bonds at
30:59
orthogonal to the to the reaction rate we can just calculate the vibrational partition function the rotational partition function all that stuff using the conventional methods that we already know about OK so now
31:11
I really rewrite write this in terms of this guy right here look at those Katie rage New now that's right there is the rest of the partition function this skewer the line over here all right and I'm getting close to being able to calculate this guy this is the contribution of along the reaction cordon only yes yes this is all the rest of it yes but OK sorry Our expression for the rate constant becomes less and we're just plugging now this expression in 4 this
31:48
equilibrium constant the double-decker on all right so we can
31:53
actually when we do that we can cancel this frequency paid
31:58
turns out we don't need to know what it is it cancels for God's sake but we don't have to measure it right we get this expression
32:07
right here and this is the same as airing equation but we derived it going way too
32:16
fast in about 20 minutes but here's the suspect
32:22
that it's very important equation now
32:31
why is it so important yeah I it we find K using cake
32:48
refined that using Mackay he the and all that can OK this could be
32:56
confusing me that Bolton's
32:58
ensconced story this is the rate constant phenomenal logical rate constant for the route for the reaction is that is the equilibrium constant that we calculate using this
33:10
expression right here ,comma right there the whole thing now you might
33:21
ask Are you going be called upon on the final exam to calculate all of this stuff no but I have to be able to sleep at nite and so I am going to disclose all of this information to you even tho I don't think it would be fair meeting write a question you
33:42
have to calculate all if you look at the end of this lecture when I IPOs this lecture after class it
33:48
doesn't that like 120 slides in the last 20 slides are a calculation that allows you to calculate the rate constant for H plus to goes to age 2 was at the very 1st reaction was studied using this equation we can work out exactly what the rate constant is if we had enough time we would do it but we don't so if you're interested In this way theory stuff this transition state there you might want to slow down the those lights were never going to get to him today it doesn't matter it does
34:24
matter but OK so here's the airing the equation but I'm just substituting Alpha 4 K double dagger here but and here's the Arrhenius equation you see that parallels the
34:42
activation energy is this delta he 0 that we were talking about the difference in the 0 . energies for
34:47
reactants some products this
34:51
pre exponential factor a that we've never said anything about that's given by this collection of variables right here party over-age times this guy right what's left over from the partition function we
35:07
stripped out From the from the normal partition function for the transition state we strip out the part of it that pertains to the vibration along the reaction coordinate
35:16
and that's what's left over because remember that that frequency just canceled for us we don't need to know what that's a good thing
35:25
because who knows what it is but how would you measure it you have to have some exotic spectroscopic method to do that OK so the Arrhenius
35:36
equation is a special case of the Eyring equation right and we can
35:43
calculate these things and if you don't believe me go to slide 101
35:47
and we go through and we do it laboriously forward a particular reaction we're not going to say more about sadly right
35:59
here are creates financial factors you can calculate this 1 actually it is calculated later
36:06
in this lecture right we can calculate
36:09
the spree exponential factors for the Arrhenius equation knowing transition state theory so it's very powerful
36:17
cocaine what we do in the last 15 minutes something very important what we want
36:24
applies this ain't thinking to a reaction that occurs in wild OK and the
36:35
key point is that we want to think about what the influence of charge is on the reaction rate it's not inconceivable that there could be a question like this on the file for
36:47
example to chlorides react with let's give led chloride all of these things can be In solution but let chloride has some solubility in water
36:56
very low all right what rate
36:59
with this reaction takes but what is the influence of the charge on the reaction rate you might say naively
37:08
if the reaction products opposite charged an ecologically attracted 1 another near action greatly accelerated but if you don't think about this too hard even if you think about it harder you might come to that conclusion right negatively charged reactants and possibly charge reactants are going to be politically attracted and following the react really fast that's going to accelerate the reaction rate but that turns out to be exactly wrong it's important to understand why all right it's great once in a while in chemistry when you encounter a concept that is completely counterintuitive at 1st later on hopefully into it all
37:53
right so I'm going to make this happen like 12 minutes here's the idea a reactor media products that's the charge on a NBC and that's the charge the key point here is
38:03
reacting surcharge so there's
38:07
a version of transition state theory but it's not strictly speaking transition state periods of thermodynamic version of it you can
38:14
use transition state theory in its normal form to describe reactions and solution because it doesn't account for reactions with solvent all right if it doesn't transition state theory its normal form does not account for the complexities imparted by having the solvent present in the reactions are episode this is a this looks like princesses a theory but strictly speaking it's something that's related to it not exactly the same thing I fighters
38:45
notation wouldn't call this math rights on noticed something if we would if we think about
38:50
this in terms of transition state theory when it reacts with the
38:53
if we form a transition state the transition state will
38:56
have a toll charge equal to a plus B right but the toll charge the transition state will be the sum of the charges on
39:06
a and B because charges to be conserved here that's a key point OK so the reason water right this is the reaction rate now in terms of this is just that we concentrate their this is a normal phenomenon than logical rate that we were right for this reaction but while OK so
39:36
then we have to think back and remember something about activities activities are going to be
39:41
the key to understanding how this works right the activity of
39:48
some guy in a musical to concentration time some activity coefficient Gamma sub all right that's the activity of air that the activity coefficient the activity coefficient for a neutral is 1 right the activity
40:06
coefficient only deviates from 1 is a consequence of colonic interactions with the solution other lines in the solution right if other lines the president solution the activity coefficient will be less than 1 of the more Alliance the lower the activity coefficient and
40:26
there's something called the about limiting lot that's the activity coefficient that's the ionic strength the ionic strength it's just given by this expression with this is the concentration of the iron sorry this is the concentration of the iron and this is the charge on the iron for every in in the solution I add up all the lines the solution multiplied by the square of the charge take at times one-half and about the ionic strength but the higher
40:57
the ionic strength it's not
40:58
and never obvious to me when equation has a allotted and it like this the higher the ionic strength the lower gamma
41:09
0 Gamma is 1 this is the ionic strength on this axis this is down on its axis if ionic strength is 0 Gamma 1 are indeed deviates from 1 as the ionic strength goes on and that the size of his deviation here depends on what the charges on the island interest all right because pursues its charge right so that a charge of 1 there's a small deviation charge of right that's the size if it's small you get a little bit bigger deviation of the charge goes up to 4 major Huge deviations bright so
41:55
I too many effects have everything to do with charge How many of you
42:12
this is review for all you got good so when we read in good years of
42:19
equilibrium constantly right in terms of activities every activities cover sometimes a concentration you guys
42:24
all know that and what's more
42:30
important is you have intuition about what the influence of lions are on equilibria here's
42:38
a partner important piece of intuition that everybody should have in the room especially those of you took my class if you look at some
42:46
equilibrium like this are right
42:53
formic acid see the gas
42:55
citric acid dissociate the Hydro Eli animosity right
43:01
if if I don't sodium chloride into the solution wonder what's going to happen to the pH sodium chloride and inert sold sodium chloride has no acidity or basic city of itself all right and yet the pH will change in a predictable way what will How many people think the pH is going to go down this is get more acidic How many people think the
43:28
pH is going to go up to give more basic when I had salt get
43:36
those hands way up there at
43:41
Thank you guys never had 151 from me now if you add
43:50
salt to this equilibrium it will always shift to the right it'll always shift to the
43:57
right the addition of a nurse salt and equilibrium always shifted the direction of the most ionic state of the equilibrium see others
44:06
irons here and there are no alliance here right that's the most ionic stay if I add salt the reaction will shift to the right it's called
44:20
assaulting and by now I can
44:22
prove that might use the equilibrium constant this reaction here there activity coefficients the activity coefficients for the neutrals are 0 1 rather idea to be cooperative with this guy's 1 can be covered the skies 1 these activity coefficients for the charge species are
44:43
and they will become lower as I increase the ionic strength solution those guys will get smaller OK
44:56
so so what that means is that the equilibrium constant that applies if we think about this activity effects it's going to get
45:03
bigger if these guys get smaller that gets bigger that the activity coefficient that applies to me and sodium
45:09
chloride to the solution or any other units sold I it's going to get more
45:15
acidic what about this guy what happens to the solubility of led sulfide I sodium chloride solutions sodium
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chloride doesn't appear this this equilibrium asked why would it
45:29
affect this equilibrium and yet it does in a predictable way what's going to happen is that led sulfide more soluble were less soluble when I dump sodium chloride more all
45:46
right why because look this side of the equilibrium is lot of alliance decides got no alliance if I add more lines to the solution
45:54
equilibrium is favored but the addition of more finance and I can
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prove that's true by working out what the new equilibrium constant is that these are the 2 activity coefficients they both gets smaller when I add sodium chloride so equilibrium customers which to shift to the right right every time you see
46:17
an equilibrium you can affect its position by adding in a salt or removing an inert salt from the solution that also altered the equilibrium a predictable way OK
46:33
what is always have to do with the transition state theory very simple To make a long story short we can work out the
46:45
map Boris escape over here because we're almost out of time here's
46:55
the bottom line the transition
46:58
state has the total charge Of the reactants and alright if the transition state it has a high then the weight of the reactions to be influenced by by the presence of other irons in the solution so that at the end of the
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day when we're done during the derivation we get this equation right here which is the equation for the kinetics salt affect what is this big pay right here it's just the collection Of the activity coefficients for the transition state and the reactants OK
47:42
they're not is the rate constant that applies for 1 more everything that's
47:48
what's gonna 0 1 and that the
47:52
actual rate constant at the reactions OK so this is the
47:59
most important slide that has to do with the 2nd concept here
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part what my plotting here this is the reaction rate for reaction involves a with
48:12
some charge pleasant with some charged going on to products
48:17
right and this is the ionic strength right so the key point here is we want understand how
48:23
salt affects the reaction rate where it's easy to understand how salt affects the reaction equilibrium constant how does it affect the reaction rate the way to think
48:34
about that is 80 reacted B and they both have a plus to charge the ball positively chargeable got plus 2 charge the
48:45
transition state has a charge plus itself there's an equilibrium between the transition state and the reactants it's going to be favored by the addition of sold the reaction is gonna get accelerated Is that counterintuitive the reaction
49:04
rate goes as I add salt To the solution even tho the reactors the products of the same charge they have overcome
49:13
Colombian barrier to react because ball positively charged the reaction rate goes up not down check this
49:22
out if a two-plus iron reacts with the 2 -minus Ryan you expected to be big
49:29
colonic attraction right reaction should go faster it
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goes all you have to do so will host
49:40
of transition stage position which is absolutely not know there are no 0 that's it not of that question but the answer is no
49:58
how bad this everybody see what has
49:59
happened so there's an equilibrium Allstate Allstate also this 1 last time that I have any more time but there's an equilibrium between a and B right the reactants and the transition state all right what we just agreed on is that we can decide which side of the equilibrium will be favored when we add salt to an equilibrium the most ionic state of the system is favored OK so if the if the charge on the transition state is higher than the charge only the 1 of the irons because the only way they can be true that the alliance said the charge of the same signed like plus 1 plus 2 plus 2 plus 2 plus 1 plus 1 right then the charge transistors it'll be like 384 and so on the transition state it's favored by the addition of salt
50:53
OK in reaction rate goes up looking goes up here to like goes up here also all right if if there is no charge nothing happens and if the charges on the on the reactants are opposite to 1 another than the charge
51:07
the transition state law the charge on the alliance the transition state has a law ionic it's it's it's the the least ionic state of the system the reactants are more ionic the transition state and the reaction is slowed
51:22
down by the addition of that's
51:27
told Lee counterintuitive if you understand that you understand something that most contests even are going to get wrong right you can get right principles charges the reaction slower you can figure out so
51:44
on Friday and there's more here yeah it's 0 my goodness riders like 20 more slides
51:54
that works through the equal revenue of rights on Friday where work on the final please take the course evaluations right