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JEE Main 2022 (24 Jun, Shift 1) · Molecular Speeds & Maxwell Distribution

Molecular Speeds & Maxwell Distribution question from JEE Main 2022 (24 Jun, Shift 1)

Q57JEE Main 2022 · 24 JUN · SHIFT 1Medium

Molecular Speeds & Maxwell Distribution

0.056 kg of Nitrogen is enclosed in a vessel at a temperature of 127∘^\circ C. The amount of heat required to double the speed of its molecules is ____________ k cal.

(Take R = 2 cal mole−1{}^{-1} K−1{}^{-1})

Numerical answer type. Work it out, then open the answer.

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Answer: 12

  1. n=5628=2n = \dfrac{56}{28} = 2 mol, T1=127+273=400T_1 = 127 + 273 = 400 K.
  2. v∝Tv \propto \sqrt{T}, so doubling the speed needs T2=4T1=1600T_2 = 4T_1 = 1600 K, ΔT=1200\Delta T = 1200 K.
  3. Gas is in a closed vessel (constant volume), N2_2 is diatomic: CV=52R=5C_V = \dfrac{5}{2}R = 5 cal mol−1^{-1}K−1^{-1}.
  4. Q=nCVΔT=2×5×1200=12000Q = nC_V\Delta T = 2 \times 5 \times 1200 = 12000 cal
  5. So the heat required is 1212 kcal.
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