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NEET 2008
Exam
NEET
Year
2008
Subject
Chemistry
Chapter
Chemical Kinetics

NEET 2008 · Chemistry · Chemical Kinetics

The bromination of acetone that occurs in acid solution is...

The bromination of acetone that occurs in acid solution is represented by this equation. CH3COCH3(aq)+Br2(aq)⟶CH3COCH2Br(aq)+H+(aq)+Br−(aq)\mathrm{CH}_3 \mathrm{COCH}_3(a q)+\mathrm{Br}_2(a q) \longrightarrow \mathrm{CH}_3 \mathrm{COCH}_2 \mathrm{Br}(a q)+\mathrm{H}^{+}(a q)+\mathrm{Br}^{-}(a q) These kinetic data were obtained for given reaction concentrations.
Initial concentrations, M</td><td></td></tr><tr><td></td><td></td></tr><tr><td>[CH3COCH3]</td><td>[Br2]</td><td>[H+]</td><td>Initialrate,disappearanceofBr2,Ms−1</td></tr><tr><td>0.30</td><td>0.05</td><td>0.05</td><td>5.7×10−5</td></tr><tr><td>0.30</td><td>0.10</td><td>0.05</td><td>5.7×10−5</td></tr><tr><td>0.30</td><td>0.10</td><td>0.10</td><td>1.2×10−4</td></tr><tr><td>0.40</td><td>0.05</td><td>0.20</td><td>3.1×10−4\begin{array}{c|l|l|l} {\left[CH_3 COCH_3\right]}</td><td>{\left[Br_2\right]}</td><td>{\left[H^{+}\right]}</td><td>Initial rate, disappearance of Br_2, Ms^{-1}</td></tr><tr><td>0.30</td><td>0.05</td><td>0.05</td><td>5.7 \times 10^{-5}</td></tr><tr><td>0.30</td><td>0.10</td><td>0.05</td><td>5.7 \times 10^{-5}</td></tr><tr><td>0.30</td><td>0.10</td><td>0.10</td><td>1.2 \times 10^{-4}</td></tr><tr><td>0.40</td><td>0.05</td><td>0.20</td><td>3.1 \times 10^{-4} \end{array}$
Based on these data, the rate equation is

Options

  1. ARate $=k\left[\mathrm{CH}_3 \mathrm{COCH}_3\right]\left[\mathrm{H}^{+}\right]
  2. BRate =k\left[\mathrm{CH}=\mathrm{COCH}$_3\right]\left[\mathrm{Br}_2\right]
  3. CRate $=k\left[\mathrm{CH}_3 \mathrm{COCH}_3\right]\left[\mathrm{Br}_2\right]\left[\mathrm{H}^{+}\right]^2
  4. DRate $=k\left[\mathrm{CH}_3 \mathrm{COCH}_3\right]\left[\mathrm{Br}_2\right]\left[\mathrm{H}^{+}\right]

Correct answer

A. Rate $=k\left[\mathrm{CH}_3 \mathrm{COCH}_3\right]\left[\mathrm{H}^{+}\right]

Step-by-step solution

Key Idea : By comparing the rate and concentration the order of the reaction can be calculated Let the rate of the reaction wrt [CH3COCH3]\left[\mathrm{CH}_3 \mathrm{COCH}_3\right], \left[\mathrm{Br}_2\right]and[H+]and \left[\mathrm{H}^{+}\right] are x,yandzx, y and z respectively. Thus, Rate ∝[CH3COCH3]x[Br2]y[H+]z5.7×10−5=[0.30]x[0.05]y[0.05]z5.7×10−5=[0.30]x(0.10)y(0.05)z1.2×10−4=[0.30]x(0.10)y(0.10)z3.1×10−4=[0.40]x(0.05)y(0.20)z\text{Rate } \propto\left[\mathrm{CH}_3 \mathrm{COCH}_3\right]^x\left[\mathrm{Br}_2\right]^y\left[\mathrm{H}^{+}\right]^z 5.7 \times 10^{-5}=[0.30]^x[0.05]^y[0.05]^z 5.7 \times 10^{-5}=[0.30]^x(0.10)^y(0.05)^z 1.2 \times 10^{-4}=[0.30]^x(0.10)^y(0.10)^z 3.1 \times 10^{-4}=[0.40]^x(0.05)^y(0.20)^z From Eqs (i) and (ii) y=0y=0 From Eqs (ii) and (iii) z=1z=1 From Eqs (i) and (iv) x=1x=1 Thus, rate law \propto\left[\mathrm{CH}_3 \mathrm{COCH}_3\right]\left[\mathrm{H}^{+}\right] =k\left[\mathrm{CH}_3 \mathrm{COCH}_3\right]\left[\mathrm{H}^{+}\right]
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