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NEET CHEMISTRYMedium

The bromination of acetone that occurs in acid solution is represented by this equation: CH3COCH3(aq)+Br2(aq)CH3COCH2Br(aq)+H+(aq)+Br(aq)\text{CH}_3\text{COCH}_3(aq) + \text{Br}_2(aq) \rightarrow \text{CH}_3\text{COCH}_2\text{Br}(aq) + \text{H}^+(aq) + \text{Br}^-(aq) These kinetic data were obtained for given reaction concentrations:

| [CH3COCH3][\text{CH}_3\text{COCH}_3] (M) | [Br2][\text{Br}_2] (M) | [H+][\text{H}^+] (M) | Initial rate, disappearance of Br2\text{Br}_2 (M s1\text{M s}^{-1}) | | :---: | :---: | :---: | :---: | | 0.300.30 | 0.050.05 | 0.050.05 | 5.7×1055.7 \times 10^{-5} | | 0.300.30 | 0.100.10 | 0.050.05 | 5.7×1055.7 \times 10^{-5} | | 0.300.30 | 0.100.10 | 0.100.10 | 1.2×1041.2 \times 10^{-4} | | 0.400.40 | 0.050.05 | 0.200.20 | 3.1×1043.1 \times 10^{-4} |

Based on these data, the rate equation is:

A

Rate=k[CH3COCH3][H+]\text{Rate} = k [\text{CH}_3\text{COCH}_3] [\text{H}^+]

B

Rate=k[CH3COCH3][Br2]\text{Rate} = k [\text{CH}_3\text{COCH}_3][\text{Br}_2]

C

Rate=k[CH3COCH3][Br2][H+]2\text{Rate} = k [\text{CH}_3\text{COCH}_3][\text{Br}_2][\text{H}^+]^2

D

Rate=k[CH3COCH3][Br2][H+]\text{Rate} = k [\text{CH}_3\text{COCH}_3][\text{Br}_2][\text{H}^+]

Step-by-Step Solution

Let the rate law be Rate=k[CH3COCH3]x[Br2]y[H+]z\text{Rate} = k[\text{CH}_3\text{COCH}_3]^x[\text{Br}_2]^y[\text{H}^+]^z.

Comparing experiment 1 and 2: When [Br2][\text{Br}_2] is doubled (0.05 M0.05 \text{ M} to 0.10 M0.10 \text{ M}) while keeping other concentrations constant, the rate remains unchanged (5.7×105 M s15.7 \times 10^{-5}\text{ M s}^{-1}). Thus, the order with respect to Br2\text{Br}_2 is 0 (y=0y = 0).

Comparing experiment 2 and 3: When [H+][\text{H}^+] is doubled (0.05 M0.05 \text{ M} to 0.10 M0.10 \text{ M}) keeping other concentrations constant, the rate is approximately doubled (from 5.7×1055.7 \times 10^{-5} to 1.2×1041.14×1041.2 \times 10^{-4} \approx 1.14 \times 10^{-4}). Thus, the order with respect to H+\text{H}^+ is 1 (z=1z = 1).

Comparing experiment 1 and 4: [CH3COCH3][\text{CH}_3\text{COCH}_3] is increased by 4/34/3 times (0.300.30 to 0.400.40), [Br2][\text{Br}_2] is unchanged, and [H+][\text{H}^+] is increased by 44 times (0.050.05 to 0.200.20). The rate becomes 3.1×1045.7×1055.44\frac{3.1 \times 10^{-4}}{5.7 \times 10^{-5}} \approx 5.44 times the initial rate. Based on the previously determined orders, the expected new rate would be proportional to the changes: Rate4=Rate1×(0.400.30)x×(0.200.05)1\text{Rate}_4 = \text{Rate}_1 \times \left(\frac{0.40}{0.30}\right)^x \times \left(\frac{0.20}{0.05}\right)^1 3.1×104=5.7×105×(43)x×43.1 \times 10^{-4} = 5.7 \times 10^{-5} \times \left(\frac{4}{3}\right)^x \times 4 (43)x=3.1×1045.7×105×4=3.122.81.36\left(\frac{4}{3}\right)^x = \frac{3.1 \times 10^{-4}}{5.7 \times 10^{-5} \times 4} = \frac{3.1}{22.8} \approx 1.36 Since 431.33\frac{4}{3} \approx 1.33, we get x=1x = 1.

Therefore, the overall rate equation is Rate=k[CH3COCH3]1[Br2]0[H+]1=k[CH3COCH3][H+]\text{Rate} = k[\text{CH}_3\text{COCH}_3]^1[\text{Br}_2]^0[\text{H}^+]^1 = k[\text{CH}_3\text{COCH}_3][\text{H}^+].

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