A. Work done in reversible, isothermal expansion of 2 mol of ideal gas from 2text dm^3$2\text{ dm}^{3}$ to 20text dm^3$20\text{ dm}^{3}$ at 300 K.
I. 4
B. Work done in irreversible isothermal expansion of 1 mol ideal gas from 1text m^3$1\text{ m}^{3}$ to 3text m^3$3\text{ m}^{3}$ at 300 K against a constant pressure of 3kPa.
II. 11.5
C. Change in internal energy for adiabatic expansion of a 1 mol ideal gas with change of temperature = 320 K and overlineC_v = frac32R$\overline{C}_{v} = \frac{3}{2}R$
III. 6
D. Change in enthalpy at constant pressure of 1 mole ideal gas with change of temperature = 337 K and overlineC_p = frac52R$\overline{C}_{p} = \frac{5}{2}R$
IV. 7
Choose the correct answer from the option given below:
### Core Logic
Evaluate each option one by one:
**Option (A)**: Work done in reversible isothermal expansion
W = -nRT lnleft(fracV_2V_1right)$W = -nRT \ln\left(\frac{V_2}{V_1}\right)$
Magnitude = frac2 times 8.314 times 3001000 times ln(10)text kJ$= \frac{2 \times 8.314 \times 300}{1000} \times \ln(10)\text{ kJ}$= 4.9884 times 2.303 approx 11.5text kJ$= 4.9884 \times 2.303 \approx 11.5\text{ kJ}$
So, A rightarrow$\rightarrow$ II.
**Option (B)**: Work done in irreversible isothermal expansion against constant external pressure
W = -P_textext (V_2 - V_1)$W = -P_{\text{ext}} (V_2 - V_1)$
Magnitude = 3text kPa times (3 - 1)text m^3 = 3 times 10^3text Pa times 2text m^3 = 6000text J = 6text kJ$= 3\text{ kPa} \times (3 - 1)\text{ m}^3 = 3 \times 10^3\text{ Pa} \times 2\text{ m}^3 = 6000\text{ J} = 6\text{ kJ}$
So, B rightarrow$\rightarrow$ III.
**Option (C)**: Change in internal energy
Delta U = n C_v Delta T$\Delta U = n C_v \Delta T$
Magnitude = 1 times left(frac32 times 8.314right) times 320 = frac12.471 times 3201000text kJ approx 3.99text kJ approx 4text kJ$= 1 \times \left(\frac{3}{2} \times 8.314\right) \times 320 = \frac{12.471 \times 320}{1000}\text{ kJ} \approx 3.99\text{ kJ} \approx 4\text{ kJ}$
So, C rightarrow$\rightarrow$ I.
**Option (D)**: Change in enthalpy
Delta H = n C_p Delta T$\Delta H = n C_p \Delta T$
Magnitude = 1 times left(frac52 times 8.314right) times 337 = frac20.785 times 3371000text kJ approx 7text kJ$= 1 \times \left(\frac{5}{2} \times 8.314\right) \times 337 = \frac{20.785 \times 337}{1000}\text{ kJ} \approx 7\text{ kJ}$
So, D rightarrow$\rightarrow$ IV.
### Step 1: Final Matching
Matches are A-II, B-III, C-I, D-IV.
### Pattern Recognition
Standard match-list question. Calculate A and D first, as they quickly eliminate wrong options.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Chemistry: Thermodynamics
Keywords:#Thermodynamic Process#JEE Main 2026 Morning Q60#Thermodynamics JEE Main 2026#Work and Internal Energy JEE Main 2026
More Thermodynamics Previous-Year Questions
Q68jee_main_2026_21_jan_morningWork Done in PV Graph
Which of the following graphs between pressure ‘P’ versus volume ‘V’ represent the maximum work done?
A.textOption 1$\text{Option 1}$
B.textOption 2$\text{Option 2}$
C.textOption 3$\text{Option 3}$
D.textOption 4$\text{Option 4}$
Solution
### Core Logic
The magnitude of work done by or on a gas is given by the area under the P-V curve projected onto the volume axis.
Graph 1: Cyclic process forming a triangle. Area is bounded, represents net work.
Graph 2: Isochoric drop (vertical line at V=22.4L$V=22.4L$). Area = 0, so work done is zero.
Graph 3: Expansion process forming a cycle. Area is enclosed in a convex shape.
Graph 4: Direct expansion from V=22.4$V=22.4$ to V=44.8$V=44.8$ at pressure P=1$P=1$ up to P=2$P=2$ (a rectangle combined with a triangle). The total area under the upper curve from V=22.4$V=22.4$ to V=44.8$V=44.8$ covers the entire shaded region under the path down to the V-axis.
Option (4) provides the largest total area under the curve extending down to the horizontal axis (maximum magnitude of work done).
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Chemistry: Thermodynamics
Q69jee_main_2026_21_jan_morningGibbs Free Energy and Equilibrium
For the reaction, N_2O_4 rightleftharpoons 2NO_2$N_{2}O_{4} \rightleftharpoons 2NO_{2}$, graph is plotted as shown below. Identify correct statements.
A. Standard free energy change for the reaction is -5.40text kJ mol^-1$-5.40\text{ kJ mol}^{-1}$.
B. As Delta G^ominus$\Delta G^{\ominus}$ in graph is positive, N_2O_4$N_{2}O_{4}$ will not dissociate into NO_2$NO_{2}$ at all.
C. Reverse reaction will go to completion.
D. When 1 mole of N_2O_4$N_{2}O_{4}$ changes into equilibrium mixture, value of Delta G = -0.84text kJ mol^-1$\Delta G = -0.84\text{ kJ mol}^{-1}$.
E. When 2 mole of NO_2$NO_{2}$ changes into equilibrium mixture, Delta G$\Delta G$ for equilibrium mixture is -6.24text kJ mol^-1$-6.24\text{ kJ mol}^{-1}$.
A plot of Gibbs free energy against the fraction of N2O4 dissociated.
Choose the correct answer from the options given below :
A.textD and E only$\text{D and E only}$
B.textC and E only$\text{C and E only}$
C.textA and D only$\text{A and D only}$
D.textB and C only$\text{B and C only}$
Solution
### Core Logic
Let's analyze the statements based on the given Gibbs free energy (G) vs. extent of reaction plot.
A plot of Gibbs free energy against the fraction of N2O4 dissociated.
A. Standard free energy change (Delta_r G^circ$\Delta_r G^{\circ}$) is the difference between standard free energies of pure products (point B) and pure reactants (point A): Delta_r G^circ = G_B^circ - G_A^circ$\Delta_r G^{\circ} = G_B^{\circ} - G_A^{\circ}$. Since B is higher than A, Delta_r G^circ$\Delta_r G^{\circ}$ is positive, not -5.40text kJ mol^-1$-5.40\text{ kJ mol}^{-1}$. Statement A is false.
B. Even if Delta_r G^circ$\Delta_r G^{\circ}$ is positive, the minimum of the curve (equilibrium state E) lies between the pure reactant and product states. Therefore, partial dissociation occurs to reach equilibrium. It is false to say it will not dissociate at all. Statement B is false.
C. The minimum E is not at fraction = 0 or 1, meaning an equilibrium mixture exists. Reverse reaction does not go to completion. Statement C is false.
D. From 1 mole of pure reactant (point A) to the equilibrium mixture (point E), the drop in Gibbs energy is 0.84text kJ mol^-1$0.84\text{ kJ mol}^{-1}$. Thus Delta G = -0.84text kJ mol^-1$\Delta G = -0.84\text{ kJ mol}^{-1}$ is correct. Statement D is true.
E. The difference from pure products (point B, equivalent to 2 moles NO_2$NO_2$) to equilibrium (E) is the entire vertical distance. The drop from B to A is 5.40$5.40$, and A to E is 0.84$0.84$. So drop from B to E is - (5.40 + 0.84) = -6.24text kJ mol^-1$- (5.40 + 0.84) = -6.24\text{ kJ mol}^{-1}$. Statement E is true.
### Step 1: Final Conclusion
Only statements D and E are correct.
### Pattern Recognition
The free energy of mixing creates a minimum 'dip' (Equilibrium) below both pure reactants and pure products, preventing either forward or reverse reactions from going absolutely to 100% completion.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Chemistry: Thermodynamics
Class 11 Chemistry: Equilibrium
Q73jee_main_2026_21_jan_morningGibbs Free Energy and Equilibrium Constant
One mole each of A_2(g)$A_{2}(g)$ and B_2(g)$B_{2}(g)$ are taken in a 1L closed flask and allowed to establish the equilibrium at 500K.
A_2(g) + B_2(g) rightleftharpoons 2AB(g)$$A_{2}(g) + B_{2}(g) \rightleftharpoons 2AB(g)$$
The value of x (in textkJ mol^-1$\text{kJ mol}^{-1}$) is .... (Nearest integer)
(Given: log K=2.2, R=8.314text J K^-1text mol^-1$\log K=2.2, R=8.314\text{ J K}^{-1}\text{ mol}^{-1}$)
Q56jee_main_2026_21_jan_eveningBond Enthalpy and Enthalpy of Atomization
Consider the following data:
Delta_f H^ominus(textmethane, g) = -X text kJ mol^-1$\Delta_f H^{\ominus}(\text{methane, g}) = -X \text{ kJ mol}^{-1}$
Enthalpy of sublimation of graphite = Y text kJ mol^-1$= Y \text{ kJ mol}^{-1}$
Dissociation enthalpy of textH_2 = Z text kJ mol^-1$\text{H}_2 = Z \text{ kJ mol}^{-1}$
The bond enthalpy of textC-H$\text{C-H}$ bond is given by:
A.(1) \ fracX + Y + 2Z4$(1) \ \frac{X + Y + 2Z}{4}$
B.(2) \ fracX + Y + 4Z2$(2) \ \frac{X + Y + 4Z}{2}$
C.(3) \ X + Y + Z$(3) \ X + Y + Z$
D.(4) \ frac-X + Y + Z4$(4) \ \frac{-X + Y + Z}{4}$
Solution
### Core Logic
Reaction for formation of methane:
textC(texts) + 2textH_2(textg) rightarrow textCH_4(textg)$$\text{C}(\text{s}) + 2\text{H}_2(\text{g}) \rightarrow \text{CH}_4(\text{g})$$-X = (Delta H_textsub text of carbon) + 2 times (textB.E. of H-H) - 4 times (textB.E. of C-H)$-X = (\Delta H_{\text{sub}} \text{ of carbon}) + 2 \times (\text{B.E. of H-H}) - 4 \times (\text{B.E. of C-H})$-X = Y + 2Z - 4(textB.E. of C-H)$-X = Y + 2Z - 4(\text{B.E. of C-H})$
### Step 1: Rearranging for Bond Enthalpy
Rearranging the equation for C-H bond enthalpy:
textB.E. of C-H = fracX + Y + 2Z4$$\text{B.E. of C-H} = \frac{X + Y + 2Z}{4}$$
### Pattern Recognition
Sees: bond enthalpy derivation from heat of formation, sublimation, and dissociation.
Trap: Sign convention errors when substituting formation enthalpies.
### Chapter Mix
Class 11 Chemistry: Chemical Thermodynamics
More Thermodynamics Questions — jee_main_2026_22_january_morning
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