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Chemical Kinetics and Nuclear Chemistry question

2023 · 8 Apr · Shift 1 · Q15
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Chemical Kinetics and Nuclear Chemistry question

2023 · 8 Apr · Shift 1 · Q15

JEE MainChemistryChemical Kinetics and Nuclear ChemistryNumerical+4 / −1
The number of given statement/s which is/are correct is ‾\underline{\hspace{2cm}}​. (A) The stronger the temperature dependence of the rate constant, the higher is the activation energy. (B) If a reaction has zero activation energy, its rate is independent of temperature. (C) The stronger the temperature dependence of the rate constant, the smaller is the activation energy. (D) If there is no correlation between the temperature and the rate constant then it means that the reaction has negative activation energy.
Numerical answer
View written solutionFree

Correct answer: 2

  1. Use the Arrhenius equation

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

Taking logarithm:

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

This shows how the rate constant kkk depends on temperature TTT and activation energy EaE_aEa​.

  1. Interpret temperature dependence

From Arrhenius equation, for larger EaE_aEa​, the exponential term changes more strongly with temperature. Hence, greater temperature dependence of kkk means larger activation energy.

So:

  • (A) Correct
  • (C) Incorrect
  1. Check statement (B)

If Ea=0E_a = 0Ea​=0, then

k=Ae0=Ak = A e^0 = Ak=Ae0=A

So kkk becomes independent of temperature provided AAA is taken constant in the Arrhenius form, which is the standard interpretation in such questions.

Hence:

  • (B) Correct
  1. Check statement (D)

If there is no correlation between temperature and rate constant, then effectively kkk does not change with TTT.

From Arrhenius equation, that corresponds to:

Ea=0E_a = 0Ea​=0

not negative activation energy.

For negative activation energy, rate constant typically decreases with increasing temperature, so there is still a temperature dependence, just opposite in sign.

Therefore:

  • (D) Incorrect
  1. Count correct statements

Correct statements are:

A,BA, BA,B

So the number of correct statements is:

222

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