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Chemical Kinetics and Nuclear Chemistry question

2022 · 30 Jun · Shift 1 · Q18
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Chemical Kinetics and Nuclear Chemistry question

2022 · 30 Jun · Shift 1 · Q18

JEE MainChemistryChemical Kinetics and Nuclear ChemistryNumerical+4 / −1
For the reaction P →\to→ B, the values of frequency factor A and activation energy EA are 4 ×\times× 1013 s −-− 1 and 8.3 kJ mol −-− 1 respectively. If the reaction is of first order, the temperature at which the rate constant is 2 ×\times× 10 −-− 6 s −-− 1 is ‾×\underline{\hspace{2cm}}\times​× 10 −-− 1 K. (Given : ln 10 = 2.3, R = 8.3 J K −-− 1 mol −-− 1, log2 = 0.30)
Numerical answer
View written solutionFree

Correct answer: 225

  1. Use the Arrhenius equation for a first-order reaction:

k=Ae−Ea/(RT)k = A e^{-E_a/(RT)}k=Ae−Ea​/(RT)

Taking natural logarithm:

ln⁡k=ln⁡A−EaRT\ln k = \ln A - \frac{E_a}{RT}lnk=lnA−RTEa​​

So,

EaRT=ln⁡(Ak)\frac{E_a}{RT} = \ln\left(\frac{A}{k}\right)RTEa​​=ln(kA​)

  1. Substitute the given values:

A=4×1013 s−1,k=2×10−6 s−1A = 4 \times 10^{13}\ \text{s}^{-1}, \qquad k = 2 \times 10^{-6}\ \text{s}^{-1}A=4×1013 s−1,k=2×10−6 s−1

Hence,

Ak=4×10132×10−6=2×1019\frac{A}{k} = \frac{4 \times 10^{13}}{2 \times 10^{-6}} = 2 \times 10^{19}kA​=2×10−64×1013​=2×1019

Thus,

ln⁡(Ak)=ln⁡(2×1019)=ln⁡2+19ln⁡10\ln\left(\frac{A}{k}\right) = \ln(2 \times 10^{19}) = \ln 2 + 19\ln 10ln(kA​)=ln(2×1019)=ln2+19ln10

Given:

ln⁡10=2.3,log⁡2=0.30\ln 10 = 2.3, \qquad \log 2 = 0.30ln10=2.3,log2=0.30

Since ln⁡2=2.3×log⁡2=2.3×0.30=0.69\ln 2 = 2.3 \times \log 2 = 2.3 \times 0.30 = 0.69ln2=2.3×log2=2.3×0.30=0.69,

ln⁡(Ak)=0.69+19(2.3)=0.69+43.7=44.39\ln\left(\frac{A}{k}\right) = 0.69 + 19(2.3) = 0.69 + 43.7 = 44.39ln(kA​)=0.69+19(2.3)=0.69+43.7=44.39

  1. Now use:

EaRT=44.39\frac{E_a}{RT} = 44.39RTEa​​=44.39

Given:

Ea=8.3 kJ mol−1=8300 J mol−1,R=8.3 J K−1mol−1E_a = 8.3\ \text{kJ mol}^{-1} = 8300\ \text{J mol}^{-1}, \qquad R = 8.3\ \text{J K}^{-1}\text{mol}^{-1}Ea​=8.3 kJ mol−1=8300 J mol−1,R=8.3 J K−1mol−1

So,

83008.3 T=44.39\frac{8300}{8.3\,T} = 44.398.3T8300​=44.39

1000T=44.39\frac{1000}{T} = 44.39T1000​=44.39

T=100044.39≈22.5 KT = \frac{1000}{44.39} \approx 22.5\ \text{K}T=44.391000​≈22.5 K

  1. The question asks for the value in the form:

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

Since

22.5 K=225×10−1 K22.5\ \text{K} = 225 \times 10^{-1}\ \text{K}22.5 K=225×10−1 K

Therefore, the required integer is:

225\boxed{225}225​

  1. Comparison with stored correct answer:

Stored correct answer = 225225225.

Our derived answer matches it.

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