Thermodynamics NEET PYQs (1990–2026)

Solved Thermodynamics PYQs

3 recent questions with answers. The full set of 100 is free to practise.

1. NEET 2026EasyWork, Heat & Internal Energy
   Q1

   Two moles of an ideal gas undergo free expansion from $10L$ to $100L$ at $300K$. The values of $\Delta S_{system}$ and $\Delta S_{surroundings}$ are: (R is universal gas constant)

   • A$\Delta S_{system}=0;\Delta S_{surroundings}=0$
   • B$\Delta S_{system}=4.606R;\Delta S_{surroundings}=-4.606R$
   • C$\Delta S_{system}=0;\Delta S_{surroundings}=4.606R$
   • D$\Delta S_{system}=4.606R;\Delta S_{surroundings}=0$

   Show answer & solution

   Correct answer: (D)

   Free expansion: $q=0,w=0$, so $\Delta U=0$. For ideal gas,
   
   $\Delta T=0$ (isothermal).
   
   $\Delta S_{system}=nR\ln \left(\frac{V_2}{V_1}\right)=2R\ln \left(\frac{100}{10}\right)=2R\ln 10=4.606R$.
   
   Since free expansion is irreversible and adiabatic,
   
   $\Delta S_{surroundings}=0$.
2. NEET 2026MediumSpontaneity & Gibbs Free Energy
   Q2

   Consider the following reaction: $2A(g)+B(g)\to 2D(g)$
   
   $\Delta U^{\Theta }=-10{\text{kJ mol}}^{-1}$ and $\Delta S^{\Theta }=-44{\text{J K}}^{-1}$ at 298 K. Identify the correct option with $\Delta G^{\Theta }$ for the reaction and spontaneity of the reaction at 298 K. (Given: $R=8.31{\text{J mol}}^{-1}{\text{K}}^{-1}$)

   • A$-1.635{\text{kJ mol}}^{-1}$, spontaneous
   • B$-0.63568{\text{kJ mol}}^{-1}$, spontaneous
   • C$+0.63568{\text{kJ mol}}^{-1}$, non-spontaneous
   • D$+1.635{\text{kJ mol}}^{-1}$, non-spontaneous

   Show answer & solution

   Correct answer: (C)

   $\Delta n_g=2-(2+1)=-1$.
   
   $$\Delta H=\Delta U+\Delta n_{g}RT=-10+(-1)\times \frac{8.31\times 298}{1000}$$
   
   $$=-10-2.48=-12.48$$
   
   kJ/mol.
   
   $$\Delta G=\Delta H-T\Delta S=-12.48-298\times \frac{-44}{1000}$$
   
   $$=-12.48+13.112=+0.632$$
   
   kJ/mol. Positive, so non-spontaneous.
3. NEET 2025HardHess’s Law & Enthalpy Changes
   Q3

   The standard heat of formation, in $kcal/mol$ of ${Ba}^{2+}$ is :[Given : standard heat of formation of ${SO}_4^{2-}$ ion $(aq)=-216kcal/mol$, standard heat of crystallisation of ${BaSO}_4(s)=-4.5kcal/mol$, standard heat of formation of ${BaSO}_4(s)=-349kcal/mol$ ]

   • A+133.0
   • B+220.5
   • C-128.5
   • D-133.0

   Show answer & solution

   Correct answer: (C)

   Let's consider the following equations:
   Formation of ${SO}_4^{2-}$ :
   $$S+2O_2+2e^{-}⟶{SO}_4^{2-}\Delta H_f=-216kcal/mol$$
   
   Crystallization of ${BaSO}_4(s)$ :
   
   $${Ba}^{2+}(g)+{SO}_4^{2-}(g)⟶{BaSO}_4(s)\Delta H_{\text{crystallisation }}=-4.5kcal/mol$$
   
   Formation of ${BaSO}_4(s)$ :
   
   $$Ba+S+2O_2⟶{BaSO}_4(s)\Delta H_f\left({BaSO}_4\right)=-349kcal/mol$$
   
   We need to find the standard heat of formation for ${Ba}^{2+}$.
   To determine this, apply the following relationship derived from the equations:
   
   $$Ba(s)⟶{Ba}^{2+}(g)+2e^{-}$$
   
   Using the data provided:
   Start from equation (3), then subtract equations (1) and (2):
   
   $$-349-(-4.5)-(-216)$$
   
   Simplifying the expression:
   
   $$\begin{array}{cc}& -349+4.5+216\\ & =-349+220.5\\ & =-128.5kcal/mol\end{array}$$
   
   This calculation shows that the standard heat of formation for ${Ba}^{2+}$ is $-128.5kcal/mol$.

Topic-wise question count

Where NEET has asked from Thermodynamics, most frequent first.

• Enthalpy & Heat Capacity30
• Work, Heat & Internal Energy29
• Hess’s Law & Enthalpy Changes28
• Spontaneity & Gibbs Free Energy6
• Entropy & Second Law5
• First Law of Thermodynamics2

Year-wise Thermodynamics questions in NEET

Number of questions from this chapter in each year's paper(s).