NEET Chemistry Chemical Kinetics Questions Solved

NEET - 2008

The bromination of acetone that occurs in acid solution is represented by this equation.

CH3COCH3(aq) + Br2(aq)            CH3COCH2Br(aq) + Br-(aq)

These kinetic data were obtained for given reaction concentrations. 

                   Initial concentrations, M

  CH3COCH3                Br2         H+

       0.30                        0.05           0.05

       0.30                        0.10           0.05

       0.30                        0.10           0.10

       0.40                        0.05           0.20

Initial rate, disappearance of Br2, Ms-1

                        5.7X10-5

                        5.7X10-5

                        1.2X10-4

                        3.1X10-4

Based on these data, the rate equation is

(a) Rate = k [CH3COCH3] [H+]

(b) Rate = k [CH=COCH3][Br2]

(c) Rate = k [CH3COCH3][Br2][H+]2

(d) Rate = k [CH3COCH3][Br2][H+]

(a) Key Idea : By comparing the rate andconcentration, the order of the reaction can be
calculated.
Let the rate of the reaction Wrt [CH3COCH3], [Br2] and [H+] are x, y and z respectively. Thus,

        Rate [CH3COCH3]x [Br2]yH+z

     5.7 x 10-5 = [0.30]x [0.05]y [0.05]z    ...(i)
     5.7 x 10-5 = [0.30]x [0.10]y [0.05]z    ...(ii)
     1.2 × 10-4 = [0.30]x [0.10]y [0.10]z   ...(iii)
     3.1 x 10-4 = [0.40]x [0.05]y [0.20]z   ...(iv)
From Eqs (i) and (ii)

                            y = 0
From eqs (ii) and (iii)

                            z = 1
from eqs (i) and (iv)
                            x = 1

Thus, rate law  [CH3COCH3] [H+]
                       = k [CH3COCH3] [H+]

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