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NEET 2026
Exam
NEET
Year
2026
Subject
Chemistry
Chapter
Thermodynamics (C)

NEET 2026 · Chemistry · Thermodynamics (C)

Consider the following reaction : 2A (g) + B (g) arrow 2D (g) Δ U^...

Consider the following reaction :
2A (g)+B (g)→2D (g)2\text{A (g)} + \text{B (g)} \rightarrow 2\text{D (g)}
ΔU⊖=−10\Delta U^{\ominus} = -10 kJ mol−1^{-1} and ΔS⊖=−44\Delta S^{\ominus} = -44 J K−1^{-1} at 298298 K.
Identify the correct option with ΔG⊖\Delta G^{\ominus} for the reaction and spontaneity of the reaction at 298298 K.
(Given : R=8.31R = 8.31 J mol−1^{-1} K−1^{-1})

Options

  1. A−1.635-1.635 kJ mol−1^{-1}, spontaneous
  2. B−0.63568-0.63568 kJ mol−1^{-1}, spontaneous
  3. C+0.63568+0.63568 kJ mol−1^{-1}, non-spontaneous
  4. D+1.635+1.635 kJ mol−1^{-1}, non-spontaneous

Correct answer

C. +0.63568+0.63568 kJ mol−1^{-1}, non-spontaneous

Step-by-step solution

The change in the number of moles of gaseous species is:

Δng=np−nr=2−(2+1)=−1\Delta n_g = n_p - n_r = 2 - (2 + 1) = -1

The standard enthalpy change ΔH⊖\Delta H^{\ominus} is given by:

ΔH⊖=ΔU⊖+ΔngRT\Delta H^{\ominus} = \Delta U^{\ominus} + \Delta n_g R T

Substituting the given values:

ΔH⊖=−10+(−1)×(8.31×10−3)×298\Delta H^{\ominus} = -10 + (-1) \times (8.31 \times 10^{-3}) \times 298

ΔH⊖=−10−2.47638=−12.47638 kJ mol−1\Delta H^{\ominus} = -10 - 2.47638 = -12.47638 \text{ kJ mol}^{-1}

The standard Gibbs free energy change ΔG⊖\Delta G^{\ominus} is:

ΔG⊖=ΔH⊖−TΔS⊖\Delta G^{\ominus} = \Delta H^{\ominus} - T \Delta S^{\ominus}

ΔG⊖=−12.47638−298×(−44×10−3)\Delta G^{\ominus} = -12.47638 - 298 \times (-44 \times 10^{-3})

ΔG⊖=−12.47638+13.112=+0.63562 kJ mol−1\Delta G^{\ominus} = -12.47638 + 13.112 = +0.63562 \text{ kJ mol}^{-1}

Since ΔG⊖>0\Delta G^{\ominus} > 0, the reaction is non-spontaneous.

Answer: +0.63568+0.63568 kJ mol−1^{-1}, non-spontaneous
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