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Chemical Kinetics · Class 12 · CBSE · Science Chemistry

A first-order reaction has a rate constant 1.15 times 10^{-3} s^{-1}. How long will 5 g of this reactant take to reduce to 3 g?

Practice question from Chemical Kinetics (Class 12 · CBSE · Science Chemistry), with the correct answer and a step-by-step solution.

medium · MCQ · Q-92D7DA

A first-order reaction has a rate constant 1.15×10−31.15 \times 10^{-3} s−1^{-1}. How long will 5 g of this reactant take to reduce to 3 g?

  1. A.444 sCorrect answer
  2. B.510 s
  3. C.650 s
  4. D.398 s

Solution

Using the first-order integrated rate equation: t=2.303klog⁡[A]0[A]=2.3031.15×10−3log⁡53=2003×(0.5228−0.4771)≈2000×0.2218=444t = \frac{2.303}{k} \log\frac{[A]_0}{[A]} = \frac{2.303}{1.15 \times 10^{-3}} \log\frac{5}{3} = 2003 \times (0.5228 - 0.4771) \approx 2000 \times 0.2218 = 444 s.

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