Thermodynamics — JEE Main PYQs (Chemistry)

ChemistryJEE Main 21 Jan 2026, Shift 1·Q18·MCQ·Easy–moderate

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Pressure volume work

Which of the following graphs between pressure ‘P' versus volume ‘V' represent the maximum work done ?

(1)
(2)
(3)
(4)

ChemistryJEE Main 21 Jan 2026, Shift 1·Q19·MCQ·Moderate

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Gibbs energy and equilibrium

For the reaction,

\ce{N2O4 <=> 2NO2}

, graph is plotted as shown below. Identify correct statements.

(A)Standard free energy change for the reaction is $-5.40$ kJ mol $^{-1}$ .
(B)As $\Delta G^\ominus$ in graph is positive, $\ce{N2O4}$ will not dissociate into $\ce{NO2}$ at all.
(C)Reverse reaction will go to completion.
(D)When 1 mole of $\ce{N2O4}$ changes into equilibrium mixture, value of $\Delta G^\ominus = -0.84$ kJ mol $^{-1}$
(E)When 2 mole of $\ce{NO2}$ , changes into equilibrium mixture, $\Delta G^\ominus$ for equilibrium mixture is $-6.24$ kJ mol $^{-1}$ .

Choose the correct answer from the options given below :

(1)D and E only
(2)C and E only
(3)A and D only
(4)B and C only

We corrected a printing error in the original paper

Source printed “As AG $^\ominus$ in graph is positive” and printed statement E twice.

ChemistryJEE Main 21 Jan 2026, Shift 1·Q23·Numerical·Moderate

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Gibbs energy and equilibrium constant

Use the following data :

Substance	$\dfrac{\Delta_\mathrm{f}H^\ominus(500\,\mathrm{K})}{\mathrm{kJ\,mol^{-1}}}$	$\dfrac{S^\ominus(500\,\mathrm{K})}{\mathrm{J\,K^{-1}\,mol^{-1}}}$
AB(g)	32	222
$\ce{A2}$ (g)	6	146
$\ce{B2}$ (g)	X	280

One mole each of $\ce{A2}$ (g) and $\ce{B2}$ (g) are taken in a 1L closed flask and allowed to establish the equilibrium at 500K.

$\ce{A2(g) + B2(g) <=> 2AB(g)}$

The value of X (in kJ mol $^{-1}$ ) is . (Nearest integer)

(Given: $\log K = 2.2$ , $R = 8.3$ J K $^{-1}$ mol $^{-1}$ )

We corrected a printing error in the original paper

Source printed “The value of x” (the table names the quantity X).

ChemistryJEE Main 21 Jan 2026, Shift 2·Q6·MCQ·Easy–moderate

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Bond enthalpy from formation enthalpy

Consider the following data:

$\Delta_\mathrm{f}H^\ominus$ (methane, g) $= -X$ kJ mol $^{-1}$

Enthalpy of sublimation of graphite $= Y$ kJ mol $^{-1}$

Dissociation enthalpy of $\ce{H2}$ $= Z$ kJ mol $^{-1}$

The bond enthalpy of C – H bond is given by:

(1) $\dfrac{X+Y+2Z}{4}$
(2) $\dfrac{X+Y+4Z}{2}$
(3) $X+Y+Z$
(4) $\dfrac{-X+Y+Z}{4}$

ChemistryJEE Main 22 Jan 2026, Shift 1·Q10·MCQ·Moderate

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Work internal energy and enthalpy

Match the LIST-I with LIST-II

List-I: Thermodynamic Process		List-II: Magnitude in kJ
A.	Work done in reversible, isothermal expansion of 2 mol of ideal gas from 2 dm $^3$ to 20 dm $^3$ at 300 K.	I.	4
B.	Work done in irreversible isothermal expansion of 1 mol ideal gas from 1 m $^3$ to 3 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 $\bar{C}_\mathrm{V} = \dfrac{3}{2}R$ .	III.	6
D.	Change in enthalpy at constant pressure of 1 mole ideal gas with change of temperature = 337 K and $\bar{C}_\mathrm{P} = \dfrac{5}{2}R$ .	IV.	7

Choose the correct answer from the option given below :

(1)A-III, B-II, C-IV, D-I
(2)A-II, B-III, C-I, D-IV
(3)A-I, B-II, C-III, D-IV
(4)A-II, B-I, C-III, D-IV

ChemistryJEE Main 22 Jan 2026, Shift 1·Q25·Numerical·Moderate

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Gibbs energy and degree of dissociation

Dissociation of a gas $\ce{A2}$ takes place according to the following chemical reactions. At equilibrium, the total pressure is 1 bar at 300K.

$\ce{A2(g) <=> 2A(g)}$

The standard Gibbs energy of formation of the involved substances has been provided below:

Substance	$\Delta G_\mathrm{f}^\circ$ / kJ mol $^{-1}$
$\ce{A2}$	$-100.00$
A	$-50.832$

The degree of dissociation of $\ce{A2(g)}$ is given by $(x\times10^{-2})^{1/2}$ where $x$ = . (Nearest integer).

[Given : $R = 8$ J mol $^{-1}$ K $^{-1}$ , $\log 2 = 0.3010$ , $\log 3 = 0.48$ ]

We corrected a printing error in the original paper

Source printed the table heading as “ $\Delta G_\mathrm{t}^\circ$ ” (subscript t for f, formation).

ChemistryJEE Main 22 Jan 2026, Shift 2·Q22·Numerical·Easy–moderate

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Born haber cycle lattice enthalpy

If the enthalpy of sublimation of Li is 155 kJ mol

^{-1}

, enthalpy of dissociation of

\ce{F2}

is 150 kJ mol

^{-1}

, ionization enthalpy of Li is 520 kJ mol

^{-1}

, electron gain enthalpy of F is

-313

kJ mol

^{-1}

, standard enthalpy of formation of LiF is

-594

kJ mol

^{-1}

. The magnitude of lattice enthalpy of LiF is kJ mol

^{-1}

(Nearest integer).

ChemistryJEE Main 23 Jan 2026, Shift 1·Q8·MCQ·Easy–moderate

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First law sign conventions

A cup of water at 5

^\circ

C (system) is placed in a microwave oven and the oven is turned on for one minute during which, the water begins to boil. Which of the following option is true ?

(1) $q = +$ ve, $w = 0$ , $\Delta U = -$ ve
(2) $q = +$ ve, $w = -$ ve, $\Delta U = +$ ve
(3) $q = -$ ve, $w = -$ ve, $\Delta U = -$ ve
(4) $q = +$ ve, $w = -$ ve, $\Delta U = -$ ve

ChemistryJEE Main 24 Jan 2026, Shift 1·Q13·MCQ·Easy–moderate

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Isothermal work reversible irreversible

Match the List-I with List-II

List-I		List-II
(Isothermal process		Work done ( $\boldsymbol{V_\mathrm{f} > V_\mathrm{i}}$ )
for ideal gas system)
A.	Reversible expansion	I.	$w = 0$
B.	Free expansion	II.	$w = -nRT\ln\dfrac{V_\mathrm{f}}{V_\mathrm{i}}$
C.	Irreversible expansion	III.	$w = -p_\mathrm{ex}\,(V_\mathrm{f} - V_\mathrm{i})$
D.	Irreversible compression	IV.	$w = -p_\mathrm{ex}\,(V_\mathrm{i} - V_\mathrm{f})$

Choose the correct answer from the options given below :

(1)A-IV, B-I, C-III, D-II
(2)A-IV, B-II, C-III, D-I
(3)A-I, B-III, C-II, D-IV
(4)A-II, B-I, C-III, D-IV

ChemistryJEE Main 24 Jan 2026, Shift 2·Q17·MCQ·Moderate

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Bond enthalpy from atomisation

The heats of atomisation of methane and ethane are ‘x' kJ mol

^{-1}

and ‘y' kJ mol

^{-1}

respectively. The longest wavelength (

\lambda

) of light capable of breaking the C-C bond can be expressed in SI unit as :

(1) $\dfrac{hc}{1000}\left(\dfrac{y-6x}{4}\right)^{-1}$
(2) $\dfrac{N_\mathrm{A}hc}{250(4y-6x)}$
(3) $\dfrac{N_\mathrm{A}hc}{250(y-6x)}$
(4) $N_\mathrm{A}hc\left(y-\dfrac{6x}{4}\right)^{-1}$

We corrected a printing error in the original paper

Source printed “The heat of atomisation of methane and ethane are”.

ChemistryJEE Main 28 Jan 2026, Shift 1·Q1·MCQ·Easy–moderate

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Isothermal reversible expansion work

20.0 dm $^3$ of an ideal gas ‘X' at 600 K and 0.5 MPa undergoes isothermal reversible expansion until pressure of the gas is 0.2 MPa. Which of the following option is correct ?

(Given: $\log 2 = 0.3010$ and $\log 5 = 0.6989$ )

(1) $w = -9.1$ kJ, $\Delta U = 0$ , $\Delta H = 0$ , $q = 9.1$ kJ
(2) $w = 9.1$ J, $\Delta U = 9.1$ J, $\Delta H = 0$ ; $q = 0$
(3) $w = +4.1$ kJ, $\Delta U = 0$ , $\Delta H = 0$ ; $q = -4.1$ kJ
(4) $w = -3.9$ kJ, $\Delta U = 0$ , $\Delta H = 0$ ; $q = 3.9$ kJ

ChemistryJEE Main 28 Jan 2026, Shift 2·Q5·MCQ·Easy–moderate

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Log k versus 1/t plot

The plot of

\log_{10}K

vs

\dfrac{1}{T}

gives a straight line. The intercept and slope respectively are (where K is equilibrium constant).

(1) $\dfrac{2.303R}{\Delta H^\circ}$ , $\dfrac{2.303R}{\Delta S^\circ}$
(2) $\dfrac{\Delta S^\circ}{2.303R}$ , $-\dfrac{\Delta H^\circ}{2.303R}$
(3) $-\dfrac{\Delta S^\circ R}{2.303}$ , $\dfrac{\Delta H^\circ R}{2.303}$
(4) $-\dfrac{\Delta H^\circ}{2.303R}$ , $\dfrac{\Delta S^\circ}{2.303R}$

ChemistryJEE Main 2 Apr 2026, Shift 1·Q4·MCQ·Moderate

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Hess law enthalpy of formation

Consider the following data

(i) $\ce{2Al(s) + 6HCl(aq) -> Al2Cl6(aq) + 3H2(g)}$ + 1200 kJ/mol.

(ii) $\ce{H2(g) + Cl2(g) -> 2HCl(g)}$ + 164 kJ/mol.

(iii) $\ce{HCl(g) + aq -> HCl(aq)}$ + 83 kJ/mol.

(iv) $\ce{Al2Cl6(s) + aq -> Al2Cl6(aq)}$ + 663 kJ/mol.

The enthalpy of formation of anhydrous solid $\ce{Al2Cl6}$ is :

(1) $-648$ kJ mol $^{-1}$
(2) $-1350$ kJ mol $^{-1}$
(3) $-2002$ kJ mol $^{-1}$
(4) $-1527$ kJ mol $^{-1}$

ChemistryJEE Main 2 Apr 2026, Shift 1·Q25·Numerical·Easy–moderate

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Gibbs energy transition temperature

At the transition temperature T,

\ce{A <=> B}

and

\Delta G^0 = 105 - 35\log T

where A and B are two states of substance X. The transition temperature in

^\circ

C when pressure is 1 atm is . (Nearest integer)

ChemistryJEE Main 2 Apr 2026, Shift 2·Q4·MCQ·Easy–moderate

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First law in cyclic process

Gas ‘A' undergoes change from state ‘X' to state ‘Y'. In this process, the heat absorbed and work done by the gas are 10 J and 18 J respectively. Now gas is brought back to state ‘X' by another process during which 6 J of heat is evolved. In the reverse process of ‘Y' to ‘X',

(1)18 J of the work is done by the gas ‘A'.
(2)2 J of the work is done by the gas ‘A'.
(3)12 J of the work is done on the gas ‘A' by the surrounding.
(4)14 J of the work is done on the gas ‘A' by the surrounding.

We corrected a printing error in the original paper

Source printed “the heat absorbed and work done by the gas is 10 J and 18 J”.

ChemistryJEE Main 4 Apr 2026, Shift 1·Q4·MCQ·Easy–moderate

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Heat capacity and first law

Given below are two statements:

Statement I : For an ideal gas, heat capacity at constant volume is always greater than the heat capacity at constant pressure.

Statement II : In a constant volume process, no work is produced and all the heat withdrawn goes into the chaotic motion and is reflected by a temperature increase of the ideal gas.

In the light of the above statements, choose the correct answer from the options given below

(1)Both Statement I and Statement II are true
(2)Both Statement I and Statement II are false
(3)Statement I is true but Statement II is false
(4)Statement I is false but Statement II is true

ChemistryJEE Main 4 Apr 2026, Shift 2·Q21·Numerical·Moderate

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Bomb calorimetry enthalpy of formation

If 3.365 g of ethanol ( $l$ ) is burnt completely in a bomb calorimeter at 298.15 K, the heat produced is 99.472 kJ. The $\lvert\Delta H_\mathrm{f}^\circ\rvert$ of ethanol at 298.15 K is $\times\,10^{2}$ kJ mol $^{-1}$ . (Nearest integer)

Given :

Standard enthalpy of combustion of graphite $= -393.5$ kJ mol $^{-1}$

Standard enthalpy of formation of water ( $l$ ) $= -285.8$ kJ mol $^{-1}$

Molar mass in g mol $^{-1}$ of C, H, O are 12, 1 and 16 respectively.

We corrected a printing error in the original paper

Answer corrected; the source key is 282 — $\Delta U_\mathrm{c} = -1359.8$ kJ mol $^{-1}$ , $\Delta H_\mathrm{c} = -1362.3$ kJ mol $^{-1}$ , $\Delta_\mathrm{f}H = -282.1$ kJ mol $^{-1}$ = $-2.82\times10^{2}$ , so the blank before “ $\times\,10^{2}$ ” is 3; also source printed “If 3.365 g of ethanol ( $l$ ) burnt completely”.

ChemistryJEE Main 4 Apr 2026, Shift 2·Q22·Numerical·Moderate

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Gibbs energy and equilibrium constant

For the following reaction at 50 $^\circ$ C and 2 atm pressure,

$\ce{2N2O5(g) <=> 2N2O4(g) + O2(g)}$

$\ce{N2O5}$ is 50% dissociated

The magnitude of standard free energy change at this temperature is x.

x = J mol $^{-1}$ [Nearest integer]

Given : $R = 8.314$ J mol $^{-1}$ K $^{-1}$ , $\log 2 = 0.30$ , $\log 3 = 0.48$ , $\ln 10 = 2.303$ , $^\circ$ C + 273 = K

We corrected a printing error in the original paper

Source printed “R = 8.314 mol $^{-1}$ K $^{-1}$ ” (unit J missing).

ChemistryJEE Main 5 Apr 2026, Shift 2·Q4·MCQ·Easy–moderate

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Gibbs energy from enthalpy entropy

Consider the following data for the reaction

$\ce{X2(g) + Y2(g) <=> 2XY(g)}$

at 600 K. The $\Delta_\mathrm{r}G^\ominus$ (in kJ mol $^{-1}$ ) for the reaction is:

Compound

\Delta_f H^\ominus_{600\,\mathrm{K}}

(kJ mol

^{-1}

)

S^\ominus_{600\,\mathrm{K}}

(J mol

^{-1}

K

^{-1}

)

XY(g)

42

200

\ce{X2}

(g)

8

140

\ce{Y2}

(g)

80

250

(1) $-21000$
(2) $-10$
(3) $-1000$
(4) $-9.012$

ChemistryJEE Main 5 Apr 2026, Shift 2·Q5·MCQ·Easy–moderate

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Molar heat capacity comparison

The correct order of molar heat capacities measured at 298 K and 1 bar is :

(1)Copper (s) $>$ Bromine (l) $>$ Helium (g)
(2)Bromine (l) $>$ Copper (s) $>$ Helium (g)
(3)Helium (g) $>$ Bromine (l) $>$ Copper (s)
(4)Helium (g) $>$ Bromine (l) $=$ Copper (s)

ChemistryJEE Main 6 Apr 2026, Shift 1·Q5·MCQ·Moderate

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Work in single and multistage processes

Arrange the following isothermal processes in order of the magnitude of the work (

p

–

V

) involved between states 1 and 2.

(A)Expansion in single stage $w_\mathrm{A}$
(B)Expansion in multi stages $w_\mathrm{B}$
(C)Compression in single stage $w_\mathrm{C}$
(D)Compression in multi stages $w_\mathrm{D}$

(1) $\lvert w_\mathrm{B}\rvert > \lvert w_\mathrm{A}\rvert > \lvert w_\mathrm{C}\rvert > \lvert w_\mathrm{D}\rvert$
(2) $\lvert w_\mathrm{C}\rvert > \lvert w_\mathrm{D}\rvert > \lvert w_\mathrm{A}\rvert > \lvert w_\mathrm{B}\rvert$
(3) $\lvert w_\mathrm{C}\rvert > \lvert w_\mathrm{D}\rvert > \lvert w_\mathrm{B}\rvert > \lvert w_\mathrm{A}\rvert$
(4) $\lvert w_\mathrm{B}\rvert > \lvert w_\mathrm{A}\rvert > \lvert w_\mathrm{D}\rvert > \lvert w_\mathrm{C}\rvert$

ChemistryJEE Main 6 Apr 2026, Shift 1·Q25·Numerical·Moderate

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Gibbs energy and equilibrium constant

Consider the reaction

\ce{X <=> Y}

at 300 K. If

\Delta H^{\theta}

and K are 28.40 kJ mol

^{-1}

and

1.8\times10^{-7}

at the same temperature, then the magnitude of

\Delta S^{\theta}

for the reaction in J K

^{-1}

mol

^{-1}

is .(Nearest Integer). (Given :

R = 8.3

J K

^{-1}

mol

^{-1}

,

\ln 10 = 2.3

,

\log 3 = 0.48

,

\log 2 = 0.30

ChemistryJEE Main 6 Apr 2026, Shift 2·Q4·MCQ·Easy–moderate

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Isothermal process work and heat

Match List-I with List-II

Given $V_1$ and $V_2$ are initial and final volumes respectively:

List-I		List-II
(Isothermal process)		(Expression)
A.	Reversible expansion	I.	$q = 0$
B.	Free expansion	II.	$q = nRT\ln\dfrac{V_2}{V_1}$
C.	Irreversible Compression	III.	$w = -p_\mathrm{ext}\left(V_2 - V_1\right)$
D.	Cyclic reversible	IV.	$\dfrac{q_\mathrm{rev}}{T} = 0$

Choose the correct answer from the options given below :

(1)A-II, B-III, C-I, D-IV
(2)A-II, B-I, C-IV, D-III
(3)A-II, B-I, C-III, D-IV
(4)A-I, B-II, C-III, D-IV

We corrected a printing error in the original paper

Source printed expression III as “ $w = -p_\mathrm{ext}(V_1 - V_2)$ ” (wrong sign for $V_1$ initial, $V_2$ final); corrected to the intended “ $w = -p_\mathrm{ext}(V_2 - V_1)$ ”.

ChemistryJEE Main 6 Apr 2026, Shift 2·Q24·Numerical·Moderate

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Gibbs energy and equilibrium constant

In a closed flask at 600 K, one mole of $\ce{X2Y4(g)}$ attains equilibrium as given below:

$\ce{X2Y4(g) <=> 2XY2(g)}$

At equilibrium, 75% $\ce{X2Y4(g)}$ was dissociated and the total pressure is 1 atm. The magnitude of $\Delta_\mathrm{r}G^\ominus$ (in kJ mol $^{-1}$ ) at this temperature is . (Nearest Integer)

(Given: $R = 8.3$ J mol $^{-1}$ K $^{-1}$ ; $\ln 10 = 2.3$ , $\log 2 = 0.3$ , $\log 3 = 0.48$ , $\log 5 = 0.69$ , $\log 7 = 0.84$ )

ChemistryJEE Main 8 Apr 2026, Shift 2·Q24·Numerical·Easy–moderate

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Enthalpy of reaction from formation

Consider the reaction :

$\ce{2H2S(g) + 3O2(g) -> 2H2O($l$) + 2SO2(g)}$

The magnitude of enthalpy change for the reaction in kJ mol $^{-1}$ is . (Nearest integer)

Given : $\Delta_f H^{\ominus}$ ( $\ce{H2S}$ ) $= -20.1$ kJ mol $^{-1}$

$\Delta_f H^{\ominus}$ ( $\ce{H2O}$ ) $= -286.0$ kJ mol $^{-1}$

$\Delta_f H^{\ominus}$ ( $\ce{SO2}$ ) $= -297.0$ kJ mol $^{-1}$