Assuming harmonic approximation, the energy change for the reaction HCl+D₂ → DCl+HD in cm⁻¹ is (the vibrational frequency data in cm⁻¹ is given in the table below),

Q69 · CSIR-NET Chemistry, June 2018

Paper: CSIR-NET June 2018 · Subject: Physical Chemistry · Chapter: Molecular Spectroscopy · Topic: Molecular Spectroscopy – General · Marks: 2 · Difficulty: Medium

Assuming harmonic approximation, the energy change for the reaction $\mathrm{HCl}+\mathrm{D}_{2} \rightarrow \mathrm{DCl}+\mathrm{HD}$ in $\mathrm{cm}^{-1}$ is (the vibrational frequency data in $\mathrm{cm}^{-1}$ is given in the table below),

HCl	$\mathrm{D}_{2}$	DCl	HD
2885	2990	1990	3627

(a)-258

(b)+258

(c)-129

(d)+129

Answer

Answer: C ✓ checked by 4AB · confidence high

Explanation

Only zero-point energies change: ΔE = ½[ν(DCl) + ν(HD) − ν(HCl) − ν(D₂)] = ½(1990 + 3627 − 2885 − 2990) = −129 cm⁻¹.

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