Thursday, March 1, 2012

Chemical kinetics blog: due 03/04/2012 @10:00pm

For a first order reaction with a rate constant k = 3.13 x 102 s-1, how long does it take for the concentration of the only reactant to become 40% of the original amount? please explain your answer...

15 comments:

  1. let [A](initial)= 100 mol/L
    so [A]= 40% of 100= 40 mol/L
    ln[A]= -kt + ln[A initial]
    ln[40]= -(3.13 x 10^2/s)t + ln[100]
    t= 2.927 x 10^-3 s

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  2. ln[A]= -kt + ln[A]initial

    k = 3.13 x 102 s-1
    t= ?
    let [A] = 100 mol/L
    then [A]initial= 40 mol/L

    ln[40] = -3.13 x 102 s-1 (t) +ln[100]

    t= .002927 = 2.927 x 10^-3 s

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  3. Since the reaction is 1st order, we use the equation:
    ln [A]t - ln [A]o = -kt
    where
    [A]t = concentration of the reactant
    [A]o = initial concentration.

    Since we are using percentage, we take a 100 mol/L sample to make the calculation simpler. Therefore, [A]t = 40 and [A]o = 100.

    So...
    ln [40] - ln [100] = -(3.13 x 10^2) x t
    t = .002927
    t = .00293

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  4. This comment has been removed by the author.

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  5. ln[A]=-kt+ln[A]initial
    ln(A/Ainitial)=-kt
    ln(40/100)=-313t
    -.91629/-313=t
    .002927=t
    t=2.927x10^-3 s

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  6. [A]initial= 100 mol/L
    [A]= 40% of 100= 40 mol/L
    the equation used is ln[A]= -kt + ln[A initial]
    plug it the numbers into the equationln[40]= -(3.13 x 10^2/s)t + ln[100]
    and finally t= 2.93 x 10^-3 s

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  7. ln [A]= -kt+ln[A]initial
    [A] initial= 100 mol/L
    [A]= 100 * .40 (40%)= 40 mol/L
    ln[40]= -(3.13x10^2 s)t+ln[100]
    t=2.927 x 10^-3 s

    ReplyDelete
  8. ln[A]=-kt+ln[A0]
    t=(ln[A]-ln[A0])/(-k)
    t=(ln[40]-ln[100]/(-3.13*10^2s)
    t=2.93*10^-3s

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  9. For a first order rxn: ln[A]=-kt+ln[A]0
    [A]=40%[A]0=.4[A]0
    ln[A]- ln[A]0=-kt
    ln([A]/ [A]0) =-kt
    ln([A]/ [A]0)/-k =t
    Plug in [A]=.4[A]0 and k=3.31x102 s-1
    ln(.4[A]0/[A]0)/(- 3.31x102 s-1)=t
    ln(.4)/(-3.31x102 s-1)=t
    (-.916)/(-3.31x102 s-1)=t
    2.93x10-3s=t

    ReplyDelete
  10. ln[A]= -kt + ln[A]initial
    k = 3.13 x 102 s-1
    let[A] = 100 mol/L
    then[A]initial= 40 mol/L
    so ln[40] = -3.13 x 102 s-1 (t) +ln[100]
    t=2.927 x 10^-3 s

    ReplyDelete
  11. Ln[A] = kt + ln[A] initial
    Ln[A] = 100 mol/L
    Ln[A] Initial = 40 mol/L
    Ln[40] = -(3.13*10^2)t + ln[100]
    t = 0.002927
    t = 2.927*10^-3 s

    ReplyDelete
  12. ln [A]= -kt+ln[A]initial
    [A] initial= 100 mol/L
    [A]= 100 * .40 (40%)= 40 mol/L
    ln[40]= -(3.13x10^2 s)t+ln[100]
    t=2.927 x 10^-3 s

    ReplyDelete
  13. ln [A]= -kt+ln[A]initial
    [A] initial= 100 mol/L
    [A]= 100 * .40 (40%)= 40 mol/L
    ln[40]= -(3.13x10^2 s)t+ln[100]
    t=2.927 x 10^-3 s

    ReplyDelete
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