Thermodynamics Previous Year Questions — NEET Chemistry

2 past-year Thermodynamics questions from NEET (Chemistry).

Q70 (2024)

At a certain temperature, T(K), during a process, 500 J is absorbed by the system and work of 200 J is done by the system. Then change in internal energy of the system is:
  1. (1) 700 J
  2. (2) 300 J
  3. (3) 400 J
  4. (4) 500 J
### Related Formula $$\Delta U = q + w$$ ### Core Logic Heat absorbed $q = +500 \text{ J}$. Work done by system $w = -200 \text{ J}$. $$\Delta U = 500 - 200 = 300 \text{ J}$$ ### Step 1: Conclusion Change in internal energy is $300 \text{ J}$. ### Pattern Recognition First Law sign convention: heat absorbed is positive, work done by system is negative. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: Thermodynamics

Q85 (2024)

Consider the following reaction: $$2A(g) + B(g) \rightarrow 2D(g)$$ $$\Delta U^{\circ} = -10 \text{ kJ mol}^{-1} \quad \text{and} \quad \Delta S^{\circ} = -44 \text{ J K}^{-1} \text{ at } 298 \text{ K}$$ Identify the correct option with $\Delta G^{\circ}$ for the reaction and spontaneity of the reaction at 298 K. (Given: $R = 8.31 \text{ J mol}^{-1} \text{K}^{-1}$)
  1. (1) $-1.635 \text{ kJ mol}^{-1}$, spontaneous
  2. (2) $+0.63568 \text{ kJ mol}^{-1}$, non-spontaneous
  3. (3) $-0.63568 \text{ kJ mol}^{-1}$, spontaneous
  4. (4) $+1.635 \text{ kJ mol}^{-1}$, non-spontaneous
### Related Formula $$\Delta H^{\circ} = \Delta U^{\circ} + \Delta n_g RT$$ $$\Delta G^{\circ} = \Delta H^{\circ} - T\Delta S^{\circ}$$ ### Core Logic $$\Delta n_g = 2 - (2 + 1) = -1$$ $$\Delta H^{\circ} = -10 - \frac{1 \times 298 \times 8.31}{1000} = -10 - 2.47638 = -12.47638 \text{ kJ/mol}$$ $$\Delta G^{\circ} = -12.47638 - \frac{298 \times (-44)}{1000} = -12.47638 + 13.112 = +0.63562 \text{ kJ/mol}$$ Since $\Delta G^{\circ} > 0$, process is non-spontaneous. ### Step 1: Conclusion $\Delta G^{\circ} = +0.63568 \text{ kJ mol}^{-1}$ and non-spontaneous. ### Pattern Recognition Positive $\Delta G^{\circ} \implies$ Non-spontaneous reaction under standard conditions. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: Thermodynamics
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JEE Physics: Waves (+15.5%) | Electrostatics: Concentric Shells (-29.7%) | Modern Physics: Photoelectric Clones (+34.2%) | Mathematics: Definite Integrals (+18.1%) | Chemistry: Coordination Splitting (-11.4%) | JEE Physics: Waves (+15.5%) | Electrostatics: Concentric Shells (-29.7%) | Modern Physics: Photoelectric Clones (+34.2%) | Mathematics: Definite Integrals (+18.1%) | Chemistry: Coordination Splitting (-11.4%)

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