Reaction mechanism and rate law | Kinetics | AP Chemistry | Khan Academy

A reaction mechanism is the sequence of elementary steps by which a chemical reaction occurs. Many reaction mechanisms contain one step that is much slower than the others; this step is known as the rate-determining step. If the rate-determining step is the first step in a mechanism, the rate law for the overall reaction can be derived directly from the stoichiometry of the step's balanced equation. View more lessons or practice this subject at www.khanacadem...
Khan Academy is a nonprofit organization with the mission of providing a free, world-class education for anyone, anywhere. We offer quizzes, questions, instructional videos, and articles on a range of academic subjects, including math, biology, chemistry, physics, history, economics, finance, grammar, preschool learning, and more. We provide teachers with tools and data so they can help their students develop the skills, habits, and mindsets for success in school and beyond. Khan Academy has been translated into dozens of languages, and 15 million people around the globe learn on Khan Academy every month. As a 501(c)(3) nonprofit organization, we would love your help!
Donate or volunteer today! Donate here: www.khanacadem...
Volunteer here: www.khanacadem...

[@gavinbranch5467]

you guys ever just sit back and wonder, how nice and smooth your life would be without chemistry. Its like a a rock in a gear box or something, that one rock just messes everything up

[@fireflymiesumae]

Indeed

[@taejgaul5991]

Me with physics

[@itsteej]

what a strange analogy but I know what you mean

[@ownitervi241]

Physics

[@sooyooso]

​@joelbackman4389doesn't work like that

[@Sp33dyBeanz]

imagine knowledge of chemistry being a puzzle, each topic/video is a puzzle piece, and this guys soothing voice is the glue that makes everytning come together and really sink in. You aint takin that puzzle apart afterwards hahahaha

[@adriannagarcia8276]

i still dont get it

[@JohnKampamba-x2g]

But how do you determine the slow and fast reaction😢?

[@dq9021]

Great. But I don't understand why the coefficient equals to the exponent in a elementary reaction.

[@stevemuigai1464]

we usually say that in an elementary step, the order is equal to the molecularity. That is a rule of thumb

[@sakshi1661]

But how to get elementary steps from given reaction

[@klukyapb5361]

@@sakshi1661 its given

[@xx_dreal_xx4319]

the rate depends upon the concentration.. the coefficient in a balanced chem eq describes the moles required to carry out the equation... form this connection in ur head.. and it becomes very clear

[@xx_dreal_xx4319]

damn i just realised iam answering a 4 year-old question lmao

[@asdfghj6300]

So how the hell do you know which one is the slow step without the " slow and fast " labeled beside the mechanisms

[@axelpedersen3715]

You compare it to the experimentally determined rate, since the fast step is so fast, it is basically negligible so the slow step (RDS) will be what matches the EDR

[@oskarjung6738]

Generally the step which involves nucleophilic attack , electrophilic attack or formation of carbocation or other intermediates are RDS.

[@adriel4040]

Could you dumb it down for me...

[@adnanmohamed6517]

That's why I don't like chemistry as much as I admire Math. In math, every step is justified and stated clearly! However, I believe chemistry is same, but the way its taught -to me at least- is sometimes frustrating by not justifying the steps.

[@rohann6199]

@Lutetium I am a JEE 2021 Aspirant bro Now I am facing the same doubt bro... Please answer me bro I request you bro

[@ochigbostella8532]

you sure did man, this video just save a soul..gracias

[@kavetopinias2317]

You're helping so much.. God 🙏 bless you..

[@OjibaDaniel-zh8xn]

Seeing this a few minutes before exam. Thanks!

[@janaisasimmons]

You didnt explain why does the rate law only mention NO2 and why is the exponent a 2.

[@ruthreinhold5645]

I love that moment in the video (7:08) when you see the slide that your professor was trying to make you believe but was not explaining, and now it suddenly makes sense

[@bhargav-gembali]

True 😂

[@vivianquevedo1662]

Thanks so much for this it was great! You explained the points I had trouble with!

[@rrgaming8248]

when you look at the elementary steps for the example question, where do you get the 2 NO2s from to begin with?

[@ahmedsarker3555]

3:22 how do you know which ones fast and which ones slow

[@krzysztofgrudzien9313]

2:45 Intermediate is not a substrate and is not a product but it IS reactant - one formed in situ :)

[@AdityaRaj-lj5wf]

Nicely.......told.

[@lakshaylakshay7019]

Very very very helpful😘

[@marynew4410]

Why is CO (g) not int the rate law? Is it because it's not in the rate determining step? Is there ever a scenario where something NOT in the rate determining step IS in the rate law (if so, why?)?

[@DimuthuYapa]

Thank you, sir.

[@hashim5395]

you saved my live in physical chemistry course

[@victoriacorcimaru1731]

Thank you so much!!!! It finally makes sence :)

[@khaiwilliams9620]

Cramming for my chemical kinetics test

[@fortniteking420sheeeesh3]

How do you know if its slow or not

[@artinaik6951]

How do you know that CO is to the zero order????

[@josiestrathman6310]

Because molecules in the zero order aren't usually listed in the final rate law equation.

[@jasmine07114]

Because the order is the exponent and if you put anything to the power of 0 then you get 1, which is why it wasn't written since 1*x=x

[@EjiguSisay]

you are best

[@karinac6944]

so helpful thank you!!!

[@ayeshaaj1787]

Thanks

[@tranquiduong2210]

you saved my life. Rrally helpful thanks a lot!!!

[@codexix8582]

Very good explanation, thanks!

[@kevinbode8464]

better than my professor

[@ruchirakukreja6127]

How do we know that we have to take NO3 in the reaction and how to predict whether the reaction is slow or fast

[@vni_]

The step in d mechanism in which an unstable intermediate product is formed is the slower one... Hope it'll help u (^_^)Ruchira

[@dudesah7422]

Couldn’t you just add the two NO2 together and make the coefficient 2?

[@nightflares3572]

But that wouldn't make the intermediate NO3 which would be used in second elementary step with CO.

[@farahratrout537]

thank youuuuu

[@RahulKumar-vz1hp]

What will.be the RDS when there two or three slow steps in a reaction.

[@7Wolf77]

Rahul Kumar which order of reaction are you talking about? Rates are zero, first and second. Having 3 or 4 or more chemical reactions could be broken down into the elementary rates. Which will be 0 through 2nd order reactions.

[@kingstarsky9739]

you can actually have negative orders too! (though they're rarely seen), but the RDS is the slowest step in a mechanism. So you simply find the slowest of the slow.

[@nightflares3572]

RDS is the slowest step in the reaction. So even though u have a lot of slow steps, the slowest one is RDS , it may be in negitive order too.

[@sharminshahbazi2591]

Can you help produce cobalt octoates?

[@TheBrokenCircuit]

How did he determine which one was the slower one?

[@crazy2pandas]

+Dinesh Kishore It is given in the problem. on the right side on the equation it usually says fast or slow

[@Cameron-hs5ry]

That is always given to you in the problem

[@kaushalsubramaniam7194]

How do we determine the elementary steps if a reaction is given and if we get the elementary steps then how do we determine the slow step from it?

[@hamzaahmed9224]

Kaushal Subramaniam same question?if u get to know the answer than plz tell me too

[@a_stumble1046]

IIRC, the slowest step has to be determined from experimentation, so it should be given in the question. That being said however, you may be able to use collision theory to determine that for example, 2 gases would react faster than 2 aqueous substances.

[@sakshi1661]

Yes same doubt bro

[@nicolewhiting7628]

For the equations do you only consider reactants

[@T_Bag069]

Yep

[@mikhalastevens7426]

What if the two elementary steps are equally fast? What would be observed to validate the mechanism?

[@nightflares3572]

It is impossible, because every reaction has its rate law , thus there would be one RDS ( slowest step in the mechanism)

[@ahzam_9]

Thanks a ton!

[@tomipurple5442]

Why its second order i don't catch it

[@ScaviDiErcolano]

How did he get NO3 in step one? (Sorry this is the only thing in chem that I can't get for some reason)

[@JohnCena-xq4kg]

NO2 + NO2 = NO + NO3 when you check both sides of the equation they are equal to each other. two nitrogen on each side and 4 oxygen on each side. when the reaction takes place NO3 is formed as a product out of NO2 and NO2. BUT it is considered an intermediate because in the next step it is consumed as a reactant

[@sccm100]

This shit is so much easier and faster than my professor

[@ozzi31o1]

Awesome video

[@khodrbouomar7448]

you saved me (midterm after 1 hour) thank you

[@annamays9064]

I love you

[@AKidNamedAlan]

Lit 🔥

[@vGoatLP]

damn this shits better than my prof

[@billygoon8926]

Gr8 vid

[@SilverXXXRaven]

wait why did he decide that that one was the slow one ?

[@RealityPlusEntertainment]

+Gabbi Zuniga Basically magic.

[@dearshoberoi285]

Gabbi Zuniga that's given in the question

[@danielkayode6870]

great

[@riancarl5239]

gahh i'm so stupid i don't understand

[@krishnenmaunick5590]

(Y)

[@jamien1620]

My AP Chem is white Jesus

[@katiewalsh4741]

Jamie Neri dude, me too

[@yacinebouziane338]

very bad explanation on this one, you're just assuming people know stuff

[@yangsun7262]

who da crap is you

[@herooftheheart6832]

just get to the point

[@sciencenerd7639]

thank you!

[@sabahatmunawar980]

Great