00:06
How can you get good at
00:09
all and no 1 good year that do not
00:14
seem to forward talk about the final exam today for me remind you that it's Tuesday
00:25
nite not Monday it's at 1 30 to 3 30 OK in this room I understand Stephen here maybe you know Jean-Marc when the review session I just checked Facebook and I didn't see you like right so if you haven't weighed in on when you want to review to be I think he's already settle on it being on Monday but of I don't think he's got the room nailed down yet and the time all right so if you haven't arrived Major opinion knowing you might want to do that are right and just stay
01:13
tuned it'll be posted on presumed by the end of the day today I don't know what I all to right about the how yes thank you it's wrong I the review is not on Saturday right now the version of this lecture that hosted the website said Saturday its balance it's on Monday OK so
01:38
this we I wrote exam yesterday know exactly what's on it so I can tell you as for problems at 15 .period I don't know why OK and
01:59
use what they are is a problem on Mack said I look at this problem founded it's similar stuff that is in Chapter
02:09
13 is it's stuff that's in Chapter 13 fears of thermal
02:15
problem that's from Chapters 14 and 15 not so
02:20
different from what you saw a mid-term 1 and then
02:25
Almaden Jr on the quiz material so you are really familiar with problems problems for reasons unconnected these last 2 problems are kinetics we haven't had
02:40
kinetics and midterm exam yet so we're going to focus this review on these last 2 problems and make sure
02:48
that we review some of this stuff where were his 2 extra credit problems over the toll of 20 points each 1 the
02:59
first one is on the transition state theory solution we
03:05
barely talk about that that was Wednesday at the end of the lecture we were rushing right so we're going to go back and look at that again we're trying to get you just 10 points to get the standpoint you've got to get the answer is exactly right there isn't a partial credit on means extra credit problems is also
03:24
stepped back problem that you see multiple times in different forms I'm
03:28
asking in a slightly different way this will not be but
03:35
something that catches you unprepared if you do any
03:39
preparation OK so that's what
03:42
it's going to be a I don't think it'll take a whole 2 hours to do
03:45
this example honestly but you'll have a whole 2 hours to do it where you can relax and make sure you get everything right double check your work right there should be plenty of time to do this exam the normal
04:00
rules apply open book open notes there will be no equations on the exam Constance conversion factors is usually you need to be able
04:07
to dig those out your book it's not
04:11
open anything else computers phones by parents solutions manuals the
04:23
books now all right part of the problem is that this work space
04:30
gets kind of congested if everybody drags in a library worth of stocks alright so you've got your book any notes that you want or fine OK that's it no other books I don't think we've enforce this on previous midterms but we're going to and enforce it on Tuesday OK any questions bring a ruler
05:03
or some sort of straight at you're going to need to draw a straight line through data points phonograph it's a hint OK
05:14
so what we want to do is we want to go back and look at the stuff that I threw at you in such haste on Wednesday right because this
05:25
is 10 points for everybody in this room if you can get this right I put this on the exam because I think it's important alright
05:36
transition state for ionic reactions in solutions here the the 3 things that we want understand 1st of all the 1st thing we want understand Is that equilibrium itself in solution depends on whether irons are present even oppose lions are not directly participating in the reaction OK equilibrium is infected or affected by the ionic strength of the solution is affected by mines that are not even reactants or products in the reaction that we care about right that's the 1st thing I understand 2nd and understand his transition state .period frivolous so in transition state theory 1 of the most important postulates is that there is an equilibrium between the reactants and a transition state all right and so
06:26
on that equilibrium like every other equilibrium that involves Lyons is perturbed by the presence of finds in the solutions all right it's not a special case right it's just another
06:39
equilibrium transferred enfeebled stressed right this
06:45
is why the presence of vines can influence the rate of reaction so here we're
06:49
talking about the equilibrium constants you are talking about the rate of reaction and the reason the rate is fact is because the equilibrium
06:57
between reactions in the transition state that equilibrium is perturbed and if the transition state is favored the if the transfer if the bionic content of the solution favors the transition state you accelerate the reaction that makes him perfect intuitive sense once you understand that way when right here
07:19
where the reactions to elusive conservatives stresses Rice sorry yes OK so the main point is that we've got charge reactants the charge on a is the year they charge on B is the the the total charge on the transition state then is the sum of the was the be right and what we're going to postulate that this transition state exists and that it's an equilibrium with these reactants right here OK and what you form this transition state it's just you know molecular reaction with rate constant K E double dagger not to pluses deformed products so we're just going to call this thing maybe
08:04
double dagger the rate of the reaction just equal to that rate constant times the concentration of the transition state yes and this is the normal way that we would write the rate of the reaction right we would just I don't know why called the key to happen but this is just the rate constant times 3 concentration of 8 times the concentration of the this is just the normal way that we write the differential rate of this reaction isn't OK so we've got that's going to come back to it intersect what we would need to understand 1st that 1st bullets that we have to understand is why ions in solution affect people agree or why
08:48
is that the case and how do we understand we talked
08:54
briefly I'll admit about activities right the activity of some molecule a which can be an iron or neutral is given by this expression right here where that's the concentration of a and there's Is the activity coefficient right the
09:11
activity coefficients not obviously the activity coefficient is 1 the activity just
09:15
across the concentration what were interested in is cases where the activity coefficient is not equal to 1 and that turns out to be
09:22
the case of is charged if a is charged in general the activity coefficient will not be equal the 1 it'll be the last so that the
09:35
activity of such as units of concentration at the activity coefficient it's got no units it's dimension us OK so this activity coefficient the Samatha we can use to calculate this is the simplest equation the equations that take up a whole screen but we're not going to pay attention to those this is the only 1 we care about that case just a constant fatigue with the 0 . 5 0 9 in water that's the
10:08
charge on the items that were calculating activity coefficient for and that is the ionic strength the ionic strength is just the concentration of each finding a solution multiplied by its charge squared Soviet
10:22
sulfate with a 2 -minus charge you be multiplied by
10:25
4 if you have sodium with a 1 plus charge to be multiplied by 1 that's just the concentration there is a term in the summation for
10:34
each and every line in the solution you just take all of the airlines the and so in the solution take the concentration
10:43
multiplied by the charge lying about multiplied by one-half that's the ionic strength that's how it's defined
10:51
OK so this is called the bicycle limiting a lot and it allows us to calculate this damn if you look at this equation you can is you can have
10:59
0 intuition about gamma write this equation doesn't it's not obvious what
11:06
damage is doing but here let me show you what this equation predicts but this equation that someone my put this is gamma on this axis right here notice that all of these curves are starting up here wine and on this axis right here that the ionic strength right so it infinite Di Lucia we're here in pure water and gamma for everything the matter what the is Gamez evil 1 now is the Ionic Strength starts the increase gamma becomes less than 1 by 1 of these different Kurds this curve right here is for and I and a cat I on an island that has a charge of 1 plus 1 or minus 1 all right it's got a size at nite right that's hydrated radius we don't need to know in detail about that but the main point is that bigger irons right show larger dynamics right see was that the scammer over a whole range of ionic strength is higher than for the Blue Guide this guy is a smaller iron that also has a charge of 1 all right so there's a negative deviations from as the ionic strength increases and if the charge goes out this is 1 this is 1 this is so worried there is a huge writers of huge
12:37
deviation from 1 that happens sport highly-charged origins right dike at Ireland's Aran Islands things like sulfate phosphate has a 3 -minus charge magnesium has a 2 plus charge designs have large activity effects if they're highly charged OK so what
13:01
we want now about this plot right here basically the activity coefficient is always less than or equal 1 it's never more than
13:14
Strength approaches 0 they should really be because it's were calling in this lecture gamma approaches 1 for any I'm yes if the Ionic Strength approaches 0 0 GAM approaches 1 OK for trolls if the molecule has no charge by definition it's Gamez equal to 1 right so whatever Gamma is describing is an electrostatic effect neutrals don't participate Downer decreases deviating more from 1 as the I get smaller yes that's this difference right here see all that's lower than that that's what I'm talking about the smaller the eye
13:55
the greater the negative deviation from what
14:00
usually intelligent use of the yet usually you can tell just by looking at an equilibrium which direction will be favored are the addition of an inert sold in other words if you change the iron content of the solution you change the ionic strength what we as Khamis 1 people understand qualitatively is what's going to happen to some equilibrium that some solution right the equilibrium in a shift to the right towards products as we add salt for example is again a shift to the left awards were not react instantly add salt as Khamis we need to have that intuition OK so let's look but take this equilibrium right here we already know that we can write the equilibrium constant for this equilibrium in terms of activities if we do that woods and writer but that would be the activity of seeing the activity of a activity to be we take damage to the sea power see the sea power would be that the power and so on but rewrite
15:19
each activity as an
15:20
activity coefficient in a concentration we don't forget these exponents we can all of these damage to 1 side Pull Along the expression now we've just got concentrations here that and we can use this collection of damage to write a concentration equilibrium constants so there's
15:39
2 kinds of equilibrium constants it turns out but you look at the back your book is
15:45
a former economic equilibrium constant this care right here it doesn't depend on the iron concentration in the solution
15:52
it's constant it really is constant the there's a K
15:58
Prime that's a concentration equilibrium constants that equilibrium constant applies specifically to a certain concentration of clients in the solution a particular ionic strength all right and includes the activity affects so this is called the concentration equilibrium constant because what you've done is used again as of now your equilibrium constants written out in terms a concentrations well that's how we
16:26
normally write it anyways but
16:29
it turns out it's only strictly correct to do this if you pull out all the scammers then you take the thermodynamic equilibrium constant multiplied by the scammers and you get the concentration equilibrium OK so by comparing the thermodynamic equilibrium constant the concentration equilibrium constant you can tell what will happen if you change the ionic strength all right if tape Prime's bigger than 10
16:56
if the concentration equilibrium constants bigger than the thermodynamic equilibrium constant that means that as you add salt equilibrium shifts towards products if the
17:07
concentration equilibrium constants last than the thermodynamic equilibrium constants that means if you add salt Everything towards
17:14
reactants but still an example all were trying to do here is qualitatively get the answer right right I want it now
17:25
here's the CD gasses but we're going to add Seoul to a city gas solution of 1 of the pH is going to go up or down you should
17:36
be able to predict that with 100 per cent accuracy every time right there's no doubt about what will happen it will not be a small change it be a change to the measure with your pH meters the pH meter was going the digits are an eclectic as you add salt dissolution so it's not a rounding error all
17:58
right here's the equilibrium constant knife killed all these Indiana's out right the gamut from Johnny and there's the gamma for acetate there's the gamma for gas in the gamma for what nominee calculate the concentration equilibrium constant for this equilibrium model I do that I just called so I take my thermodynamic equilibrium constant multiplied by these 2 guys in the numerator there they are and divide by these 2 guys there they are now that's my concentration equilibrium constant all right and then I look at these damn is here and I can already get gas how big they
18:35
are right notice these 2 guys in the numerator what's special about them the neutral
18:44
parts of their Damazer 1 by definition boom bloom
18:49
what about the bottom guys they're charged right there Damazer going to be less than 1 by definition right OK and so on just this really crude thinking here those are 1 of those are less than 1 that means that this thing in a red box here is going to be greater than 1 that means that the concentration equilibrium constants greater than the firm anemic equilibrium constant that means
19:12
if I add salt salted the solution In these guys
19:18
get smaller right when I had salt these Gamez are going to
19:21
get smaller remember because if
19:27
we're here and we add more salt would go down here these scams are smaller when ends solved in this direction right here OK these 2 gamblers with small missiles into the suitcase from a collector right now we can go through and mathematically figure this out using this approach for
19:51
any equilibrium you can do this but into the analogous thing right now what happens if the airlines on
19:58
both sides when you can't tell in other words if these guys were charged in the numerator this would be less than 1 is to be less than once you that less than 1 less than 1 less than 1 less than 1 you
20:09
can't just do a back-of-the-envelope prediction about what will happen you have to actually calculate the numerical Gamez using the device happily limiting along then you could figure out what's happening right here
20:21
were just doing sort of a meatball estimation all right which works fine allotted time turns out OK so what we're going to predict is if we add salt to the solution it's going to shift to the right we're going to solutions become more acidic Dorian concentrations going to go up the pH is going to go down that's
20:43
what actually happens what about this I
20:49
noticed something on looking at this equilibrium here what we just said is has been a shift to the right look at these guys and look at these guys which state of the system is more ionic reactants for products
21:03
products the product surcharge the reactants are neutral right it turns out that adding salt or favors the more bionic state the system here
21:16
products are more I on the reactants and so I add salt equilibrium is going the shift to the right if you just
21:25
remember that will get the right answer every time all right equilibrium favors the addition of salt to a system in equilibrium favors the most ionic state of the system yes yet it's the reactants is a more
21:44
basic yet look at this guy right and we're talking about the solubility of lead sulfide lenders also give led to plus over 2 minus which state of the system is more ionic
21:59
products again that's totally neutral right what's going to happen if I add sodium chloride to this electrolyte amazingly the LAT sulfides going to become more soluble the solubility of alleged sulfide goes up by quite a bit it's not a small
22:19
thing we neglected in Kim 1 in all Okayama in inorganic chemistry we totally sweeties effects under the carpet but they're not small effects
22:33
hotline 0 that's true I can work it out mathematically here the 2 banners for those 2 Alliance hears the case St the expression all right so that concentration equilibrium constants can be put the thermodynamic equilibrium constant abide by these 2 Gamez how big those 2 Gamez for both in the less than 1 because both of these species are charged in so when I calculate that means that this whole thing here is going to be greater than 1 but it so and when multiplied what which it was 1 of the things this is great resource brain alright so the concentration equilibrium constants going to be greater than that thermodynamic equilibrium constant guests In the solubility is going to go up we call this sulking in right hardly anybody calls it that anymore right but time analytical chemist still know what this means salting and means you add an inert
23:59
salt to a solution we're trying to get some sparingly soluble salt that's on the bottom layer Lemire trying to get that into solution it's not working what are you going to do if you can keep the solution up of course that's 1 option another option is just add
24:13
inert sold we had inert these Gamez go down the becomes smaller the solubility this this concentration equilibrium constant goes up the
24:23
solubility goes up to attractive that every old-timer notes so
24:34
absolutely yes saturation concentration goes out yeah that's that's actually what it means to say that the solubility goes up why
24:46
why does this happen this is magic is in some ways the most important thing to understand practices what Peter thereby understood when he derided by equation Colom's lot
25:00
What is this this is the energy acting between 2 irons in the solutions this is the distance these 2 wines are from 1 another the senator center distance OK as we get further and further apart the energy goes to 0 0 up here at the top right so as the linesman far apart they have no pool on
25:20
interaction but as they come closer and closer together the
25:23
energy goes down these 2 iron stabilize 1 another if they have an opposite
25:28
shot if they have the same charge the musical like this
25:33
that goes on right but the point is in solution you've got alliance there's no barrier to designs moving around the convey can go
25:44
wherever they want to wear the energy is the lowest is where they choose to go out however the arrange themselves the automatically arrange themselves like
25:52
this right you see how can I answer calls to an alliance and I encircles the Catalans alright right there's few cases were and I circles to 1 another they
26:03
don't have to be so they're not not a solution is very flexion Elian's Armenian around all over the place but on average if you take a snapshot you'll see this loose ionic Gladys exists even in Lakewood salt solutions right there's an ionic lattice that exists even In liquid salt solutions it's counterintuitive on how could there be a lattice of mines in the liquid right well it's not a
26:32
precise lattice alliance right but it's a very loose so you see this you don't see them write the solution doesn't a lot like that otherwise it would be elected statically destabilized OK so these physics exert an influence on every ionic reaction because I am want to
26:51
join this ionic collapse y because they stabilize the whole system the energy the whole system goes down when they joined the
26:58
latter yet more alliance the last it's reinforced by the energy goes down even more that's why gamma keeps going down right there's a greater and
27:12
greater electrostatic effect acting as you increase the concentration of the irons are
27:16
closer to 1 another the solution looks like there's not like this on book like this you get electrostatic static destabilization
27:27
parts of the alliance this is completely counterintuitive to me but you've got designs they can
27:34
be anywhere they want to but they form a lattice they organize themselves so they lower the electrostatic energy right and what that does is it changes the driving force for every reaction that involves clients that's what we're trying to understand what these garments but again as the walls to predict the influence of this bionic lattice on equilibrium OK so coming
28:00
back to this picture we can apply this logic now than this equilibrium but so far
28:05
we've just been talking about generic equilibria for reactions and solution now we
28:11
can come back to the rate of this reaction which is going to be influenced by this equilibrium here but because in transition state theory we postulate there's an equilibrium between transition state the reactants OK so now I can write an expression for this equilibrium constant fears the activity the transition state here's the activity of a and B I can write each activity in terms of gamma times concentration I can roll all these Gamez up into a cage gamma This is
28:40
what your book calls it it's OK
28:42
damage is the equilibrium constant for the activity coefficients if you well very strange notation to use but this is what we chose to use so that is just that collection of Gamez there OK at myself in the transition state concentration here are right this is the expression that I get is that the equilibrium constant here this is that collection of Gamez a right and about 8 times B and so the rate of the reaction is now going to be given by this expression right here OK this is your equation 20 49 age so what this says
29:25
notice very important
29:29
as this equilibrium constant gets larger the reaction accelerates what is that equilibrium constitutes the equilibrium between the transition state and reactants as that gets bigger the reaction goes faster that the transition state
29:41
their OK and by putting this
29:44
damage and the denominator we include now the
29:48
effective Sultan the solution on this equilibrium
29:53
now we're not going to go through and derive all these other equations here but this turns out to be an important 1 but what this says is that those effective second-order rate constant of the reaction
30:07
the thing that we've been calling the rate constant all along right that's
30:10
equal to the rate constant that infinite die Lucian of salt ionic strength equals 0 but the bed 0 means minus lot of Kadima and take gamma is this collection of it's that right that stadium look at this is the master equation that describes this transition state theory and solution what is this predicted on that's those guys yes that can calculate them yes we can do some algebra out yesterday drive this equation from that equation this is a better equation and it actually explicitly says what the effect of that of Katie is ongoing and strength that's 2051 here's what predicted right this plot it's
31:08
kind of hard to understand what's make sure we understand what is on the this
31:15
is the rate constant K 2 right reaction going faster in this direction slower in this direction this is the square root of the ionic strength so this is infinite dilation here and I'm adding salt adding salt insult as they go in this direction the point of this plot is to understand what happens to the reaction rate as we increase the ionic strength but what happens to the reaction rate it's a little counterintuitive I think here's the reaction rate at infinite dimension for every reaction all right if the reactor in the product at the same charge the reaction make its accelerated that's true here that's true here that's true here the amount of acceleration it depends on how charged the reactants are the more charge they are the more real reaction it's accelerated by adding salt if they have an opposite charge the reaction slows down but as I had sold by small the reaction down this bizarre but the reason this happens and it is because in this case right here look at this 1 reactants both have close to chart the transition state that will have a passport charge right that cost for
32:42
charge as a higher charge state the 2 plus 2 you might think plus 4 equals 2 plus 2 so isn't among charge the same no for transfer to choose by a higher magnitude as much stronger coupling with the ionic network in the solution than to two-plus science OK is so that
33:06
plus 4 get stabilized and the reaction that's accelerated so more salt I add the faster and faster and faster the reaction goes if I look at this guy down here this is a plus to an A-minus to what the charge in the transition state here 0 all right
33:25
so now you're creating you've got irons that a strongly coupled his ionic network measure creating a transition state that doesn't want to be in the network and doesn't care it's neutral or right the reaction
33:36
it's slowed down by the addition of salt because the reactants are stabilized so equilibrium is shifting the reactant direction they are stabilized by the solved the transition state is not reaction doesn't get accelerated so if you could understand this plot qualitatively you should be
33:58
able to get 10 points 10 extra points on the phone question yes but
34:07
that it had something to do with the money we have seen it for Klusener to minus 1 in the great question let's think about that you've got reactants plus into minus what's going to happen to that reaction accelerated the
34:30
accelerated or no effect
34:34
2 plus for minors where 4 plus 2 mines articles reactants for plus 2 minor How many people think that if I add salt to that solution I will accelerate the reaction rate
34:53
How many people think that if I had felt that solution will be the accelerate reactor at
34:59
right for plus to minus it's 6 toll charges in the reactants the
35:06
transition states can have a charge of 1 2 plus or minus I went to him see that 6 toll charges the reactants and 2 for the transition state so the reactants aridity favored the reactants are more ironic than the transition state OK if if the reactants the same charge this it's a little confusing because if you have to win to Annabel classes than the transition states for and what you have to remember is for Trump's to into but they have opposite charges that that will be the case you have it'll be obvious which 1 has OK
35:47
everyone in ghetto standpoints for a total score of 210 are so there's going to be a problem not dissimilar from this on your exam it is a graph paper concentration of but some substrates velocity and we have to be able figure out what's going on and we need to know they will calculate all the relevant parameters and the Mac's turnover number catalytic efficiency now we didn't talk about it no that's not on your exam all right this picture keeps coming up in connection with everything that we do we can get away from it right here in in this case this is not the transition state the enzyme substrate complex this is the cartoon that applies this is the rate
36:50
constant for the reaction of the enzymatic reaction right it's also the
36:56
turnover number it's also a constant case subcontract rights of your reading the literature on enzymes that means they may say k cat is this just talking about that rate constant right there all those guys have units of seconds to minus 1 because the first-order rate constants first-order Indians on substrate complex look so we worked out the the mathematics for this using the steady-state approximation this big K and here's the Mikhail constant in this connection of rate constants right here related to those guys this is what the generic enzyme reaction does right this is the reaction rate on its axis this is the substrate concentration here .period time axis and this is the concentration of the substrate of course at the substrate is 0 the reaction rate is 0 and out and substrate reaction looks first-order at 1st
37:57
OK but eventually when I fill up all the enzyme was substrate I reach of the
38:03
next this -dash line here represents what that is the Max's equal the K 2 times the initial
38:11
concentration of enzyme that I had at the beginning of the experiment the total amount of enzyme that's present in the bigger right that its
38:19
concentration there so I can calculate the Mac's a fine OK too we derived in this equation which is not called the line Beaverbrook equation but the plot that we make from a mysteriously is called the line Weaver Burke plot what is that it's a plot of 1 over substrates versus 1 over the reaction rate OK so of ideas and given substrate and the information I've got a calculator 1 over the and 1 over before I can make a
38:52
line Weaver bird plot once I've made it this intercept here
38:57
on the 1 over the axis is going to be 1 of the this interceptors won over actually minus 1 over KTM right cited the maxim came from those 2 interception right away it's really easy it's helpful if I can draw a straight line that's why that ruler here's what your plant should look like qualitatively OK you gotta get these intercepts right you get a rhythm of the grafted that they'll make a grant that looks the graphic section with a lot of points but it's important to get it right quantitatively right so you have plenty of time to make it don't worry and then once you've got it you can read it .period for for its rematch . 9 0 1 overcame and Kate the max over the concentration of enzymes but I I can calculate all this stuff make sure you get the unit's right units anywhere .period as always OK fears of an old exam here is an old exam questions consider the following reaction mechanism blah blah blah assuming steady surprise me that derive expression of reaction rate this is like the hottest steady-state problem whatever asked on an exam if you
40:34
can do this when you can do the ones on the exam on Tuesday guarantee it the 1 could be an exempt
40:41
stations and by proton Niger gasses nite acts of arson sorry reacts to probe that as a plus sign and it's hard to see here so that age to N O 2 Class H 2 and two-plus reacted bromide together all the are right here the rate constants OK so what we have to know to get this right 1st of all we have to be able pick out all the intermediates what's in the media well that I looked like an intermediate look he's here and here and he's not here so he's definitely an intermediate what else following the Oct he's here and here and he's not here OK so he's an intermediate that's why this is hard can apply the steady-state approximation twice you got applied to every intermediate OK so let's go through and do that but what he did and I don't remember who my teaching assistant was in 2010 but they didn't have very good penmanship and this is not my handwriting my handwriting is immaculate so what do you do the time rate of change of this guy that's what this right here I know you can't read that time rate of change of age 2 N O 2 class that's this he said that equal to 0 that's the 1st thing that we're looking for and then you've got have each In St. for that species represented by a term right this is the buildup but the age Allacham plus from here right protons agent to Bloomberg K 1 bird then he got the minus 1 you got the 2nd reaction here who writes you get 3 terms and now you solve the concentration of the intermediate we should really say Page 2 N O 2 plus steady states to distinguish it from the general concentration for that species that's what it's going to be able to right there right 6 points forgetting that guy right then we're going do the same thing with this guy O & B R here is set equal to 0 you did exactly the same thing source as saying Of all went beyond this case is only 2 terms 1 for that 1 for that OK but when I read it out this guy appears in this expression in so what once I've got this expression I can substitute this whole mess here In for the aged 2 and 0 2 plus I get this monster equation here which happens to be correct in this kind of monstrous you should see what it looks like if you don't apply the steady-state approximation total nightmare show but that got this guy notice that that guy is the only 1 that appears in the rate expression for the product that's the product we care about that's the guy that appears in the raid expression not this guy but this guy appears indirectly because he appears in the expression for this guy right there OK until all the rate of the reaction it's K 3 times on br Tennessee 6 685 Back at any age 2 OK and there it is plug everything in that's what the integrated that's what the differential relies for this reaction In steady state approximation OK now I can ask questions about this I can say Look what happens to that of apparent rate lies functional bromide concentration all this bromide here and bromide here write a fight increased if so of I'm a bromide large we expect this term in the denominator to dominate key minus 1 but if that dominates the bromide here will cancel all right and so I might end up with so at Highbury are these the are going cancel for us because this term K to be our dominates overcame minus-1 yards canceled I get a reaction that has overall 2nd order that doesn't depend on B AA-minus at Highbury AA-minus we shouldn't have any br minor sensitivity to the rate that makes sense
45:27
we've effectively isolated the reaction with respect to be our minds maybe online is big enough by reaction doesn't care about anymore it cares about the ones that are not carried the reactants are not very big at
45:40
low we are minus what happens groups that will that low AA-minus came minus-1 dominates this term goes away all right we have a collection of rate constants here we've got 1 2 3 concentrations OK so the reaction has overall 3rd order and it does depend on the AA-minus so this too
46:05
limiting cases you can tell there's going to be too limiting cases immediately because there's is a
46:10
plus sign in the denominator looking so what else could we talk about possibly with no other
46:22
Connecticut issues could be broached on this exam I don't really know what I mean it's you have
46:30
to be able to write the reaction rates right here the rules for doing that from an earlier lecture you have to be able to figure out what the units are on the reactor on the rate constant right you do that by just putting the units writing that 1st of all riding the differential rate expression and putting the units on the concentrations but in the units on the on the reaction rate which is always smaller per 2nd and then just solving for the units of que no matter what this thing looks like you could always get the right units of K by doing now here's an example His another example we have sorry methods for determining what the reaction rate what the differential reaction rate is but the rate lot is we have 3 methods for doing that 1 of them is the method of initial rates you make everything
47:26
all the reactants liquor in the mixture big except 1
47:32
and if you do that you isolate direction with respect to that reacted what's in this case it's a and you work out the matter for doing that this equation applies lot the reaction rate equals log of the K Prime which includes the king all the other concentration I have to make
47:50
everything big except 1 reactant in this case a did I just say that a dissident Everything big except
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1 reactor isolated that 1 reacted in this case it would be a and then you can plot Logar the reaction rate as a function of log of a and the small is just the molecular 30 of the reaction with respect but the number of
48:16
aids that are participating in a reaction you can take the reaction mechanism apart reacted by reacted by doing that OK what other options do you have we can use integrated
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rail often talked about that and you can set your data to an integrated right then there's the half-life you can if you can measure the half-life of your reaction here is an example of working out the integrated rate love for a reaction has ordered 3 halves that would be bizarre but you can work it out if you had to use without looks like right and here's the half-life In the half-life behaves the half-life itself tells you mean absolutely nothing but successive half flights tell you a lot alright the successive life goes down by a factor of 2 the reaction is first-order we have like doesn't change of soaring 0 order where half a dozen changes 1st half-life Gibson doubled on each successive have direction is 2nd order and so on and you can derive the T have expression for more complicated mechanisms if you have but OK and finally there is the Iranian's equation that tells you about the temperature dependence of the reaction rates but you have to know what the activation energy is the temperature and you have to know what is free exponential factor is or you can determine the Prix exponential factor if you want from the data that you have because the Prix exponential factors the intercept of this a Arrhenius plot of like Avis is 1 over at and that's
50:10
everything located on website even be interested in they don't want
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this bumper sticker here you're 1 of my like this 1 are possible I don't think you 1 I notice also that they have many of these know differences in different colors and sizes of application should 1 of the and this is a terrible thing to say about OK so everyone's gonna do well on Tuesday block few