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Chemical Kinetics Test - 12

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Chemical Kinetics Test - 12
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  • Question 1
    1 / -0.25

     

    The radioisotope N-13 which has a half-life of 10 min is used to image organs in the body. If the injected sample has an activity of 40 μCi (microcurie), what is the activity after 30 min?

     

    Solution

     

     

    Disintegration follows first-order kinetics
    t = total time = 30 min
    t 50 = half-life = 10 min


     

     

  • Question 2
    1 / -0.25

     

    The following data were obtained during the first order decomposition of

    2A(g) → B(g) + C(s)

    at constant volume and at a particular temperature : 

    Thus, rate constant is

     

    Solution

     

     







     

     

  • Question 3
    1 / -0.25

     

    A G .M. Counter is used to study the process of first order of radioactive disintegration. In the absence of radioactive substance A, it counts 3 dps (disintegration per second). When A is placed in G.M Counter it records 23 dps at the start and 13 dps after 10 min. It records x dps after next 10 min. Half-life period of A is y min. Thus, x and y are

     

    Solution

     

     

    When there is no radioactive substance in G.M. Counter, it records = 3 dps. Thus, it is the zero-error in the counter and in each it is added. Thus, initial counts = 23 - 3 = 20 dps.
    Attimef (after 10min) = 13- 3 = 10dps
    Thus, half-life is 10 min = y
    Hence, after next 10 min, dps = 5
    Hence, reading in G.M. Counter = 5 + 3 = 8 dps = x

     

     

  • Question 4
    1 / -0.25

     

    Inversion of sucrose (C12 H22 O11 ) is a first order reaction and is studied by measuring angle of rotation at different interval of time

    r0 = angle of rotation at the start, rt = angle of rotation at time t
    r = angle of rotation at the complete reaction

    There is 50% inversion, when

     

    Solution

     

     

    r0 = rotation at the start, rt  = rotation at time t
    r = rotation at the end then (r  - r0 ) = a and (r - rt ) = (a - x)

    When 50% inversion has taken place


    ∴ 2 (a - x) = a
    2(r - rt ) = r - r0
    2r - 2rt = r - r0
    ∴ r0 = (2rt - r )

     

     

  • Question 5
    1 / -0.25

     

    Following radioactive disintegration follows first order kinetics :

    Starting with 1 mol of A in a 1L flask at 300 K, pressure set up after two half-lifes is approximately

     

    Solution

     

     

    When B is formed from A, two a-particies (He) are formed.
    A taken initially = 1 mol

    This helium remains in closed vessel.
    Thus, pressure set up is due to helium.

     

     

  • Question 6
    1 / -0.25

     

    For the first order reaction Tav (average life), T50 (half-life) and T75 (time 75% reaction) are in the ratio of

     

    Solution

     

     




     

     

  • Question 7
    1 / -0.25

     

    For the first order reaction,


    Following equations are given :



    Select the correct equations.

     

    Solution

     

     

    For the first order reaction,










    ∴ (a-x) = a (1/2)y     (Equation II)

     

     

  • Question 8
    1 / -0.25

     

    Rate constant of a first order reaction (A →B) is 0.0693 min-1 . If initial concentration is 1.0 M, rate after 30 min is

     

    Solution

     

     

    C0 = 1 M



    ∴  

     

     

  • Question 9
    1 / -0.25

     

    Following reaction is pseudo-unimolecular w.r.t. C6 H5 N2 CI (A)

    50 mL of 1M benzene diazonium chloride (A) is taken. After 1 h, 1.226 L of N2 gas at 1 atm and 300 K is obtained. Thus, half-life of the reaction is (log 250 = 2.40) 

     

    Solution

     

     






    Half-life(t50 )= 
     

     

     

  • Question 10
    1 / -0.25

     

    Minimum half-life of an isotope needed so that not more than 0.1 % of the nuclei undergo decay during a 3.0 h laboratory experiment is

     

    Solution

     

     



     

     

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