Writing Rate Laws of Reaction Mechanisms Using The Rate Determining Step - Chemical Kinetics

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  • Опубликовано: 21 июл 2024
  • This chemistry video tutorial provides a basic introduction into reaction mechanisms within a chemical kinetics setting. It explains how to write the rate law expression for a reaction mechanism. A reaction mechanism consist of a series of elementary steps or elementary reactions whose rate law can be written from its molecularity - that is from the coefficients of the balanced reaction. The rate of a reaction mechanism is completely dependent on the slow step or the rate-determining step. This video explains how to substitute an intermediate when writing rate law expressions. It contains plenty of examples and practice problems.
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Комментарии • 274

  • @TheOrganicChemistryTutor
    @TheOrganicChemistryTutor  2 года назад +22

    Chemistry PDF Worksheets: www.video-tutor.net/chemistry-basic-introduction.html
    Full-Length Videos & Exams: www.patreon.com/MathScienceTutor/collections
    Direct Link to The Full Video: bit.ly/3vPPUad

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    @abdallaaalbeshti1192 6 месяцев назад +61

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  • @melodious_moon
    @melodious_moon 3 года назад +172

    My professor literally "taught" us this just last class... needed this! Thanks!

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    @marvinsimukonda8049 2 года назад +108

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  • @EnglishAddiction
    @EnglishAddiction 2 года назад +21

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  • @masterno8576
    @masterno8576 Год назад +113

    For everyone wondering on why it’s not 2h2o2 for the last one it’s because overall reaction is solely determined on slow process

    • @asy6515
      @asy6515 Год назад +6

      I was confused at first but thank you for clarifying that!!

    • @diamondmason8366
      @diamondmason8366 Год назад

      Thank you very much!

    • @rebeccaabraham9348
      @rebeccaabraham9348 Год назад +4

      THANKS!!! Have a chem test tmw and was confused

    • @ElisaFalsafi
      @ElisaFalsafi 9 месяцев назад

      Isn’t having I in rate equation a violation to one of the conditions? And then replace it using rate formed = rate reversed?

    • @LKOO7
      @LKOO7 4 месяца назад

      If it is soley determined on slow process, why is there no I-?

  • @sabrinapelcher6554
    @sabrinapelcher6554 3 года назад +133

    The fact that you are keeping up with me by posting these videos as I'm learning this material is perfect. Thank you

    • @ryanlyle9201
      @ryanlyle9201 3 года назад +5

      I didn't realize he's following perfectly with my course until this comment... dang

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      @Adrenadriven7 Год назад +1

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  • @pelumiemmanuel7965
    @pelumiemmanuel7965 Год назад +27

    Since the rate law is determined by the coefficient of the reactants…
    Then why is 2H2O2 written as “k[H2O2]^1” instead of “k[H2O2]^2”

    • @Kamal17824
      @Kamal17824 2 месяца назад

      That’s what I was thinking

    • @Kamal17824
      @Kamal17824 2 месяца назад +4

      Turns out it’s because we only write what the slow step is. Since the slow step only has H2O2 we only write that since we follow the slow step only

  • @oswaldodesantiago5559
    @oswaldodesantiago5559 3 года назад +23

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  • @daemonzap1481
    @daemonzap1481 3 года назад +92

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  • @sheetalkonda7280
    @sheetalkonda7280 2 года назад +31

    Question: at time 13:20
    Since there is one molecule of O3 and 2 molecules of NO2, Shouldn't k= [O3] [NO2]^2?
    Then the reaction would be first order with respect to O3, second order with respect to NO2 and third order overall?

    • @kingpyrrhusofepirus6686
      @kingpyrrhusofepirus6686 2 года назад +15

      So you only look at the rate determining step when writing rate law. The rate determining step will al always be the slow step.

    • @morathicasas7520
      @morathicasas7520 2 года назад +16

      No, the rule that you are thinking of, about the molecularity and how the coefficients equal the reactant order, only applies to "elementary reactions". It does not apply to this overall reaction because it is a multistep reaction. He says this at 9:05 . The reaction order(s) of an overall reaction that is multistep depends on the rate law of the determining step.

    • @keanupie8399
      @keanupie8399 Год назад +1

      @@kingpyrrhusofepirus6686 how do we know which is the slow step?

    • @kingpyrrhusofepirus6686
      @kingpyrrhusofepirus6686 Год назад +3

      @@keanupie8399 It's been awhile for me, but I think they will usually either give you the rates of each step, or they will simply tell you one of them is the slow step depending on the question.

    • @keanupie8399
      @keanupie8399 Год назад

      @@kingpyrrhusofepirus6686 thank you!

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    @user-yh5df1cz6o 5 месяцев назад

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  • @harmanmaur9735
    @harmanmaur9735 4 месяца назад

    definitely the best video on this concept, thank you

  • @enaman5067
    @enaman5067 3 года назад

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    can you upload some vector transformation equations too, it would be really helpful.

  • @lukerosan3302
    @lukerosan3302 2 года назад

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    @caesarwiratama3303 2 года назад

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  • @rabiamirza6821
    @rabiamirza6821 2 года назад +19

    Question for the last example wouldn’t the rate constant be= k[H2O2]^2?

    • @julianescobar1672
      @julianescobar1672 2 года назад +2

      That's what I would've thought to

    • @prestonrossi7597
      @prestonrossi7597 2 года назад +15

      It would be, except that he adds that the first step is the "slow" step, and the second step is the "fast" step. Since the slow step always determines the speed of the reaction (think "you can't go faster than the slowest person in line"), then you only use what's in the slow step, which, in this case, is just one H2O2. If it's still confusing, go back and check the previous example that he showed, and compare its answer to his first example, which didn't use the "slow" or "fast" rates.

    • @gerryaraujo7852
      @gerryaraujo7852 2 года назад +5

      For a multi-step reaction, the slow step (rate limiting/rate determining step) determines the rate of the whole chemical reaction even when your overall reaction has different molar coefficient/s. In other words, stick to the slow step at all times when writing the rate law of the reaction.

    • @KrazyBogart
      @KrazyBogart Год назад

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    • @KrazyBogart
      @KrazyBogart Год назад

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    @ugwuokechinedu8393 2 месяца назад

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    @donamikuton768 Месяц назад

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  • @quintustheophilus9550
    @quintustheophilus9550 3 года назад +2

    Thank you for the video! I was struggling with this!

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    @kauyen5187 5 месяцев назад +2

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    @shem7146 Год назад

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    @WintaWesley 7 месяцев назад

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  • @ericmora6287
    @ericmora6287 3 года назад +13

    I'm just a bit confused. So the coefficients don't matter when determining what type of overall reaction it is? How would you be able to distinguish bimolecular reaction from a unimolecular reaction?

    • @na-kumlee6317
      @na-kumlee6317 3 года назад +7

      idk if this will help but overall rate law can only be determined experimentally. So like looking at the graphs or tables. so I think concluding the order of each reactant for overall rate law was a mistake. Elementary reaction on the other hand, you can calculate by looking at molecularity. One cannot determine the order of each reactants in overall balanced equation simply by looking at coefficients. Does that help?

    • @jiinjung1445
      @jiinjung1445 3 года назад +1

      @@na-kumlee6317 Thank you!

  • @diablopm.1
    @diablopm.1 8 месяцев назад +1

    in the overall reaction, why didnt you raise the rate overall for NO2 to the power 2? maybe i missed out on something

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    @tiktokhub4298 2 года назад

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    @jonathannemeth2784 2 года назад

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    @aadygoel4837 3 года назад +1

    Perfect timing !!!]

  • @carpediem2789
    @carpediem2789 2 года назад +1

    Should the orders be experimentally determined and not by the coefficients? This is what I’ve learned in rate law. Are we just assuming that the coefficients are the order or reaction? But may show a different order in an experiment?
    Thanks

    • @elijah4145
      @elijah4145 2 года назад

      I believe in elementary reactions, the coefficients correspond to the order, although they are normally determined experimentally

  • @nazlifa7788
    @nazlifa7788 3 года назад +1

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  • @01FrozenFuze
    @01FrozenFuze 2 года назад +3

    In 13:20 wouldn't it be Fast Rate = K [ NO3 ] [ NO2 ] rather than Rate = K [ O3 ] [ NO2 ]?

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    @VirtualWorld-wv2um 9 месяцев назад +1

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    @redkritter1225 3 года назад +10

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    @ashetube5707 Год назад

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    @lightseekers2515 3 года назад

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    @aiman_shakir Год назад

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  • @kevincorrigan1754
    @kevincorrigan1754 3 года назад +2

    what happened to that other fast/slow step video where u had an example of a slow step being in the middle of the reaction? im trying to find that vid and i cant find it did you delete it? in that vid you showed us why the overall order is different from whats in the slow/fast steps, it was rlly helpful, on this one u gloss over it like in 13:18.. why is NO2 not raised to the 2nd power? :(

    • @incognito6751
      @incognito6751 3 года назад +2

      He's forcing you to pay for the longer videos now on Patreon.

    • @kxkxsxi6305
      @kxkxsxi6305 3 года назад

      NO2 isn't raised to the second power because it depends on the slow step of the reaction. Usually at this level they give you all the information about the system in the question . Rate determining step = first slow step

  • @munaawol6722
    @munaawol6722 3 года назад

    Thank u soooo much man

  • @eriknelson2559
    @eriknelson2559 2 года назад +1

    Can a fast first step ever be non-equilibrium?

  • @alfred4177
    @alfred4177 2 года назад

    Thank you soo much

  • @ahmedsarker3555
    @ahmedsarker3555 2 года назад

    12:54 for example they gave the rate and they gave the overall equation, how do we then break them down into slow reaction and fast reaction

    • @ahaf4654
      @ahaf4654 2 года назад

      They have to tell you which one is the fast step and which one is the slow step

  • @ofosuaanyarko6153
    @ofosuaanyarko6153 Год назад +1

    Please, why is the overall rate of reaction for the second question, first order?
    H2O2 has 2 Infront of it in the overall reaction.
    Please explain further, I don't get it.

  • @hocuspocus__
    @hocuspocus__ Год назад

    crazy how this dude taught me in 18 mins what my chem teacher cant do in 1 hr.... literally no explanation on the slides 😔

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    @hayatzeynu7795 3 года назад +2

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    @alitahir9822 2 года назад

    really thanu full to you☺

  • @christiatannous2877
    @christiatannous2877 3 года назад +8

    shouldn't [NO2] in the overall rate be [NO2]^2 ? since it has 2 NO2 in the equation?

    • @teacherdanz3794
      @teacherdanz3794 3 года назад +6

      The slow step in elementary reaction is considered to be the rate determining step. It is always the slow step for the basis of overall rxn. The reason why we only have [NO2] in the overall.

    • @christiatannous2877
      @christiatannous2877 3 года назад

      @@teacherdanz3794 ohh right right

    • @kjay5587
      @kjay5587 2 года назад

      @@teacherdanz3794 is the first step always the slow step?

    • @renazhamid1721
      @renazhamid1721 2 года назад

      @@kjay5587 yes

  • @kurooackerman7338
    @kurooackerman7338 3 года назад

    yo thank you so much

  • @flyorwalk1743
    @flyorwalk1743 3 года назад +10

    Wait at the end....why the rate equation doesn't become "rate=k [H2O2]^2" but only to the power of 1??

    • @taongakasanda9487
      @taongakasanda9487 3 года назад

      Yes I have also noticed, because the coefecient of the overall reaction is #2

    • @quyumkehinde2683
      @quyumkehinde2683 3 года назад +1

      I think it’s simply because we’re to consider the slow reaction, and not the overall equation.

    • @aadygoel4837
      @aadygoel4837 3 года назад

      @@quyumkehinde2683 on the contrary we are only supposed to see the slow reaction . I feel you meant slow but typed fast .

    • @quyumkehinde2683
      @quyumkehinde2683 3 года назад +1

      @@aadygoel4837 Exactly! Thank you.

    • @wajdy2620
      @wajdy2620 2 года назад

      @@quyumkehinde2683 but that is the overall reaction?

  • @calinmarie5974
    @calinmarie5974 2 года назад

    how do u know which step is slow step and which step is fast step if neither is provided

  • @kaleabyohannes7909
    @kaleabyohannes7909 3 года назад +1

    Tnx very very much

  • @walyachilz9466
    @walyachilz9466 11 месяцев назад

    For the overall reaction the NO2 has a coefficient of 2. when wrinting the rate law isnt it supposed to be to the power 2 making it 3rd order?

  • @hanasmoonlight
    @hanasmoonlight 3 года назад +7

    Idek why I'm watching this, idk wtf this is because I solely clicked on this video to hear their voice 😭✋🏻

  • @andrewjustin256
    @andrewjustin256 4 месяца назад

    18:24 Is there someone who has solved the problem number two? Would anyone please walk me through what must be done in that problem? First reaction is reversible, so how does it affect our calculations? Is the law of mass action any helpful for this somehow? Plus am I to put down the reactions separately: one the forward and the next to be backward?

  • @optimistickrishiv843
    @optimistickrishiv843 5 месяцев назад

    god bless you man

  • @tyreseblair9007
    @tyreseblair9007 3 года назад

    This would have helped me so much a year ago

  • @lovemorenkomo732
    @lovemorenkomo732 2 года назад

    Overall reaction has a coefficient of 2 on hydrogen peroxide,are we not supposed to say concentration of hydrogen peroxide raised to power 2 since there is two on the overall equation?

  • @antikahraman8248
    @antikahraman8248 3 года назад +1

    13:17 can someone explain why we did not write "2" for power of NO2 at the last rate formula?

    • @user-iv2ms2zq6c
      @user-iv2ms2zq6c 3 года назад +1

      It is based on the slow reaction, not the overall reaction. The slow reaction only has one NO2.

    • @antikahraman8248
      @antikahraman8248 3 года назад +1

      @@user-iv2ms2zq6c thank you so much .

    • @user-iv2ms2zq6c
      @user-iv2ms2zq6c 3 года назад

      @@antikahraman8248 No problem!

  • @dailysaturday1538
    @dailysaturday1538 3 года назад

    Thank yoooou

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    @LinaPhalane-tv9xu Год назад

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    @edmundtakudzwa6290 3 года назад

    Amazing

  • @origamigek
    @origamigek Год назад

    So why is the rate order directly matched with the stoichiometry? This has to be determined experimentally and cannot just be assigned like this right?

    • @origamigek
      @origamigek Год назад

      And why is iodide not in the total rate law? Surely it speeds up the reaction.

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    @jonathangurr3955 Год назад

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    @wekajakdeng4096 3 года назад +1

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    @gm-sj8iq 2 года назад

    home boy explained what my professor couldnt in less than a minute.

  • @johnathanchivington9854
    @johnathanchivington9854 2 года назад +2

    "ter" in "termolecular" is the root of "tertiary" or "third in order or level"

  • @debrizzy5638
    @debrizzy5638 Год назад +1

    Is the first step always the slow step?