NEET Previous Year Questions on Thermodynamics

Q 1 :
Choose the correct statement for the work done in the expansion and heat absorbed or released when 5 litres of an ideal gas at 10 atmospheric pressure isothermally expands into vacuum until volume is 15 litres. [2024]

both the heat and work done will be greater than zero.
heat absorbed will be less than zero and work done will be positive.
work done will be zero and heat will also be zero.
work done will be greater than zero and heat will remain zero.

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(3)

Q 2 :
For the following reaction at 300 K,

$A_{2 (g)} + 3 B_{2 (g)} \to 2 {AB}_{3 (g)}$

The enthalpy change is $+ 15 kJ$ , then the internal energy change is: [2024]

19988.4 J
200 J
1999 J
1.9988 kJ

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(1)

If $n_{p} < n_{r}$ and $Δ n_{g} = n_{p} - n_{r} = - ve$ ; then,

$Δ H < Δ E$

As $Δ H = + 15 kJ$ or $+ 15, 000 J$ , the only possible answer from the given options is 19988.4 J.

Q 3 :
The work done during reversible isothermal expansion of one mole of hydrogen gas at 25°C from pressure of 20 atmosphere to 10 atmosphere is:
(Given $R = 2.0$ $cal$ $K^{- 1}$ ${mol}^{- 1}$ ) [2024]

0 calorie
–413.14 calories
413.14 calories
100 calories

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(2)

$w = - 2.303 n R T \log \frac{V_{2}}{V_{1}}$

or $w = - 2.303 n R T \log \frac{P_{1}}{P_{2}}$

$= - 2.303 \times 1 \times 2 \times 298 \times \log \frac{20}{10} = - 413.14$ $calories$

Q 4 :
Which amongst the following options is the correct relation between change in enthalpy and change in internal energy? [2023]

$Δ H - Δ U = - Δ n R T$
$Δ H + Δ U = Δ n R$
$Δ H = Δ U - Δ n_{g} R T$
$Δ H = Δ U + Δ n_{g} R T$

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(4)

$Δ H = Δ U + Δ n_{g} R T$

Q 5 :
Which of the following P–V curve represents maximum work done? [2022]

[MAGE 31]
[MAGE 32]
[MAGE 33]
[MAGE 34]

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(2)

Q 6 :
Which one among the following is the correct option for right relationship between $C_{P}$ and $C_{V}$ for one mole of ideal gas? [2021]

$C_{V} = R C_{P}$
$C_{P} + C_{V} = R$
$C_{P} - C_{V} = R$
$C_{P} = R C_{V}$

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(3)

$C_{P} = C_{V} + n R$

For one mole of ideal gas,

$C_{P} = C_{V} + R or C_{P} - C_{V} = R$

Q 7 :
The correct option for free expansion of an ideal gas under adiabatic condition is [2020]

$q = 0, Δ T = 0 and w = 0$
$q = 0, Δ T < 0 and w > 0$
$q < 0, Δ T = 0 and w = 0$
$q > 0, Δ T > 0 and w > 0$

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(1)

For free expansion of an ideal gas, $P_{ex} = 0$ ,

$w = - P_{ex} Δ V = 0$

For adiabatic process, $q = 0$

According to the first law of thermodynamics,

$Δ U = q + w$

As internal energy of an ideal gas is a function of temperature,

$Δ U = 0, ∴ Δ T = 0$

Q 8 :
Under isothermal conditions, a gas at 300 K expands from 0.1 L to 0.25 L against a constant external pressure of 2 bar. The work done by the gas is [Given that 1 L bar = 100 J] [2019]

30 J
-30 J
5 kJ
25 J

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(2)

Expansion of a gas against a constant external pressure is an irreversible process. The work done in an irreversible process

$= - P_{ext} Δ V = - P_{ext} (V_{2} - V_{1}) = - 2 (0.25 - 0.1)$

$= - 2 \times 0.15 L bar = - 0.30 \times 100 J = - 30 J$

Q 9 :
Reversible expansion of an ideal gas under isothermal and adiabatic conditions are as shown in the figure.

[IMAGE 35]
$A B \to$ Isothermal expansion
$A C \to$ Adiabatic expansion
Which of the following options is not correct?   [2019]

$Δ S_{isothermal} > Δ S_{adiabatic}$
$T_{A} = T_{B}$
$W_{isothermal} > W_{adiabatic}$
$T_{C} > T_{A}$

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(4)

For an ideal gas, internal energy is a function of temperature. Final temperature i.e., $T_{C}$ for adiabatic process is less than its initial temperature i.e., $T_{A}$
$∴$ $T_{C} < T_{A}$

Q 10 :
An ideal gas expands isothermally from $10^{- 3} m^{3}$ to $10^{- 2} m^{3}$ at 300 K against a constant pressure of $10^{5}$ $N$ $m^{- 2}$ . The work done on the gas is [2019]

+270 kJ
-900 J
+900 kJ
-900 kJ

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(2)

$w = - P d V = - P (V_{2} - V_{1})$

$= - 10^{5} {Nm}^{- 2} (10^{- 2} - 10^{- 3}) m^{3} = - 10^{5} {Nm}^{- 2} (9 \times 10^{- 3}) m^{3}$

$= - 9 \times 10^{2} Nm = - 900$ $J$ $(∵ 1 J = 1 Nm)$

Topic Question Set

Q 1 :
Choose the correct statement for the work done in the expansion and heat absorbed or released when 5 litres of an ideal gas at 10 atmospheric pressure isothermally expands into vacuum until volume is 15 litres. [2024]

(3)

Q 2 :
For the following reaction at 300 K,

$A_{2 (g)} + 3 B_{2 (g)} \to 2 {AB}_{3 (g)}$

The enthalpy change is $+ 15 kJ$ , then the internal energy change is: [2024]

Q 3 :
The work done during reversible isothermal expansion of one mole of hydrogen gas at 25°C from pressure of 20 atmosphere to 10 atmosphere is:
(Given $R = 2.0$ $cal$ $K^{- 1}$ ${mol}^{- 1}$ ) [2024]

Q 4 :
Which amongst the following options is the correct relation between change in enthalpy and change in internal energy? [2023]

Q 5 :
Which of the following P–V curve represents maximum work done? [2022]

(2)

Q 6 :
Which one among the following is the correct option for right relationship between $C_{P}$ and $C_{V}$ for one mole of ideal gas? [2021]

Q 7 :
The correct option for free expansion of an ideal gas under adiabatic condition is [2020]

Q 8 :
Under isothermal conditions, a gas at 300 K expands from 0.1 L to 0.25 L against a constant external pressure of 2 bar. The work done by the gas is [Given that 1 L bar = 100 J] [2019]

Q 9 :
Reversible expansion of an ideal gas under isothermal and adiabatic conditions are as shown in the figure.

[IMAGE 35]
$A B \to$ Isothermal expansion
$A C \to$ Adiabatic expansion
Which of the following options is not correct?   [2019]

Q 10 :
An ideal gas expands isothermally from $10^{- 3} m^{3}$ to $10^{- 2} m^{3}$ at 300 K against a constant pressure of $10^{5}$ $N$ $m^{- 2}$ . The work done on the gas is [2019]

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Topic Question Set

Q 1 : Choose the correct statement for the work done in the expansion and heat absorbed or released when 5 litres of an ideal gas at 10 atmospheric pressure isothermally expands into vacuum until volume is 15 litres. [2024]

(3)

Q 2 : For the following reaction at 300 K, A2(g)+3B2(g)→2AB3(g) The enthalpy change is +15kJ, then the internal energy change is: [2024]

Q 3 : The work done during reversible isothermal expansion of one mole of hydrogen gas at 25°C from pressure of 20 atmosphere to 10 atmosphere is: (Given R=2.0 cal K-1mol-1) [2024]

Q 4 : Which amongst the following options is the correct relation between change in enthalpy and change in internal energy? [2023]

Q 5 : Which of the following P–V curve represents maximum work done? [2022]

(2)

Q 6 : Which one among the following is the correct option for right relationship between CP and CV for one mole of ideal gas? [2021]

Q 7 : The correct option for free expansion of an ideal gas under adiabatic condition is [2020]

Q 8 : Under isothermal conditions, a gas at 300 K expands from 0.1 L to 0.25 L against a constant external pressure of 2 bar. The work done by the gas is [Given that 1 L bar = 100 J] [2019]

Q 9 : Reversible expansion of an ideal gas under isothermal and adiabatic conditions are as shown in the figure. [IMAGE 35] AB→ Isothermal expansion AC→ Adiabatic expansion Which of the following options is not correct? [2019]

Q 10 : An ideal gas expands isothermally from 10-3m3 to 10-2m3 at 300 K against a constant pressure of 105N m-2. The work done on the gas is [2019]

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Q 1 :
Choose the correct statement for the work done in the expansion and heat absorbed or released when 5 litres of an ideal gas at 10 atmospheric pressure isothermally expands into vacuum until volume is 15 litres. [2024]

Q 2 :
For the following reaction at 300 K,

$A_{2 (g)} + 3 B_{2 (g)} \to 2 {AB}_{3 (g)}$

The enthalpy change is $+ 15 kJ$ , then the internal energy change is: [2024]

Q 3 :
The work done during reversible isothermal expansion of one mole of hydrogen gas at 25°C from pressure of 20 atmosphere to 10 atmosphere is:
(Given $R = 2.0$ $cal$ $K^{- 1}$ ${mol}^{- 1}$ ) [2024]

Q 4 :
Which amongst the following options is the correct relation between change in enthalpy and change in internal energy? [2023]

Q 5 :
Which of the following P–V curve represents maximum work done? [2022]

Q 6 :
Which one among the following is the correct option for right relationship between $C_{P}$ and $C_{V}$ for one mole of ideal gas? [2021]

Q 7 :
The correct option for free expansion of an ideal gas under adiabatic condition is [2020]

Q 8 :
Under isothermal conditions, a gas at 300 K expands from 0.1 L to 0.25 L against a constant external pressure of 2 bar. The work done by the gas is [Given that 1 L bar = 100 J] [2019]

Q 9 :
Reversible expansion of an ideal gas under isothermal and adiabatic conditions are as shown in the figure.

[IMAGE 35]
$A B \to$ Isothermal expansion
$A C \to$ Adiabatic expansion
Which of the following options is not correct? [2019]

Q 10 :
An ideal gas expands isothermally from $10^{- 3} m^{3}$ to $10^{- 2} m^{3}$ at 300 K against a constant pressure of $10^{5}$ $N$ $m^{- 2}$ . The work done on the gas is [2019]