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Chemical Kinetics and Nuclear Chemistry question

2021 · 20 Jul · Shift 1 · Q19
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Chemical Kinetics and Nuclear Chemistry question

2021 · 20 Jul · Shift 1 · Q19

JEE MainChemistryChemical Kinetics and Nuclear ChemistryNumerical+4 / −1
The inactivation rate of a viral preparation is proportional to the amount of virus. In the first minute after preparation, 10% of the virus is inactivated. The rate constant for viral inactivation is ‾×\underline{\hspace{2cm}}\times​× 10 −-− 3 min −-− 1. (Nearest integer) [Use : ln 10 = 2.303; log10 3 = 0.477; property of logarithm : log xy = y log x]
Numerical answer
View written solutionFree

Correct answer: 106

  1. Set up the kinetics equation

Since the inactivation rate is proportional to the amount of virus present, the process follows first-order kinetics:

dNdt=−kN\frac{dN}{dt} = -kNdtdN​=−kN

On integration,

N=N0e−ktN = N_0 e^{-kt}N=N0​e−kt

or

NN0=e−kt\frac{N}{N_0} = e^{-kt}N0​N​=e−kt

  1. Use the given information

In the first minute, 10% is inactivated, so 90% remains after 1 minute.

Thus,

NN0=0.9att=1 min\frac{N}{N_0} = 0.9 \quad \text{at} \quad t=1\,\text{min}N0​N​=0.9att=1min

So,

0.9=e−k(1)0.9 = e^{-k(1)}0.9=e−k(1)

Taking natural logarithm:

ln⁡0.9=−k\ln 0.9 = -kln0.9=−k

Hence,

k=−ln⁡0.9=ln⁡(109)k = -\ln 0.9 = \ln\left(\frac{10}{9}\right)k=−ln0.9=ln(910​)

  1. Evaluate numerically using the given logarithm values

We use

ln⁡(109)=ln⁡10−ln⁡9\ln\left(\frac{10}{9}\right) = \ln 10 - \ln 9ln(910​)=ln10−ln9

Now,

ln⁡9=ln⁡(32)=2ln⁡3\ln 9 = \ln(3^2)=2\ln 3ln9=ln(32)=2ln3

Given:

log⁡103=0.477\log_{10} 3 = 0.477log10​3=0.477

So,

ln⁡3=2.303×0.477\ln 3 = 2.303 \times 0.477ln3=2.303×0.477

Therefore,

ln⁡9=2(2.303×0.477)\ln 9 = 2(2.303 \times 0.477)ln9=2(2.303×0.477)

Compute:

2.303×0.477=1.0985312.303 \times 0.477 = 1.0985312.303×0.477=1.098531

Thus,

ln⁡9=2×1.098531=2.197062\ln 9 = 2 \times 1.098531 = 2.197062ln9=2×1.098531=2.197062

Now,

ln⁡10=2.303\ln 10 = 2.303ln10=2.303

Hence,

k=2.303−2.197062=0.105938k = 2.303 - 2.197062 = 0.105938k=2.303−2.197062=0.105938

So,

k≈0.106 min−1k \approx 0.106\,\text{min}^{-1}k≈0.106min−1

  1. Match with the asked format

The question asks for:

‾×10−3 min−1\underline{\hspace{2cm}} \times 10^{-3}\,\text{min}^{-1}​×10−3min−1

Since

0.106=106×10−30.106 = 106 \times 10^{-3}0.106=106×10−3

the required integer is:

106\boxed{106}106​

  1. Comparison with stored answer

Derived answer = 106106106

Stored correct answer = 106106106

They agree.

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