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Rate of reaction and coefficient of the reactan

  1. Mar 17, 2014 #1
    Suppose in the reaction 2 NO + O2 --------> 2NO2

    Why when the the concentration of NO is doubled, the rate increases 4 times, I know that the rate is directly proportional to the square of NO concentration (I don't know why) and it's order of reaction is 2 ( I don't why ). but I still can't understand a reason for all of that it seems foggy to me why the coefficient affects the proportionality. It should be intuitive to a chemistry student, I think a simple analogy would be helpful, thanks
  2. jcsd
  3. Mar 17, 2014 #2


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    Staff: Mentor

    While everything you wrote is correct, it is the wrong way around.

    First, we should check what is the reaction order - and the only sure way of doing it is an experiment. Once we know order is 2 everything else follows as a series of conclusions.
  4. Mar 17, 2014 #3

    But in elementary reactions, the order is equal to the coefficient, isn't that true and why ???
  5. Mar 17, 2014 #4


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    Staff: Mentor

    Yes it is true - because we defined it this way. Order of the reaction equals sum of the coefficients from the elementary reaction equation.
  6. Mar 17, 2014 #5


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  7. Mar 17, 2014 #6

    You really misunderstand me, I know because it's defined like that, I mean why does the number of moles in a balanced question affects the proportionality in the rate equation for an example 2NO + O2 ------> 2NO2 , I2 + H2 -----> 2HI

    Supposing that they are elementary reactions
    Why in the first equation on doubling the conc of NO the rate increases 4 times but on doubling I2 it increases only 2 times

    I already know the conception of the order of reaction and this stuff

    but I want an analogy that really clarifies it, or a detailed easy explanation that make it clear and intuitive to a high school student.
    Last edited: Mar 17, 2014
  8. Mar 17, 2014 #7


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    Staff: Mentor

    If you are looking for intuition - reactions occur when the molecules collide, the more molecules, the more frequent the collisions. Number of collisions for a given kind of a molecule is proportional to its number (or concentration).
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