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Thermodynamics · Question 15

NEET (UG) 2022MCQMedium📈 Topic in 50% papers+4−1
1

Which of the following p-V curve represents maximum work done?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]

Answer

(2) [figure]

Solution

As per NCERT, work done in an expansion is equal to the area under the p–V curve between the initial and final volumes, w = - ViVf pex dV.

⇒ In (1) the process is cyclic; the work equals only the small area enclosed by the loop.

⇒ In (3) the line is vertical, i.e., volume does not change (dV = 0), so no work is done.

⇒ In (2) and (4) the gas expands isothermally from the same high pressure, but in (2) the pressure falls slowly and the expansion goes on to a much larger volume.

∴ The area under the curve, and hence the magnitude of work done, is maximum in (2).

Answer: (2)

NEET (UG) 2022

Keep practising — Thermodynamics

2

One mole of an ideal gas at 300 K is expanded isothermally from 1 L to 10 L volume. U for this process is : (Use R = 8.314 J K-1 mol-1)

  1. 0 J
  2. 1260 J
  3. 2520 J
  4. 5040 J
NEET (UG) 2022 (Phase 2)
3

Which one among the following is the correct option for right relationship between CP and CV for one mole of ideal gas?

  1. CV = RCP
  2. CP + CV = R
  3. CP - CV = R
  4. CP = RCV
NEET (UG) 2021
4

For irreversible expansion of an ideal gas under isothermal condition, the correct option is :

  1. U 0, Stotal = 0
  2. U = 0, Stotal = 0
  3. U 0, Stotal 0
  4. U = 0, Stotal 0
NEET (UG) 2021
5

For the reaction, 2Cl(g) Cl2(g), the correct option is :

  1. r H > 0 and r S < 0
  2. r H < 0 and r S > 0
  3. r H < 0 and r S < 0
  4. r H > 0 and r S > 0
NEET (UG) 2020
6

The correct option for free expansion of an ideal gas under adiabatic condition is :

  1. q = 0, T < 0 and w > 0
  2. q < 0, T = 0 and w = 0
  3. q > 0, T > 0 and w > 0
  4. q = 0, T = 0 and w = 0
NEET (UG) 2020
7

In which case change in entropy is negative?

  1. Sublimation of solid to gas
  2. 2H(g) H2(g)
  3. Evaporation of water
  4. Expansion of a gas at constant temperature
NEET (UG) 2019
8

Under isothermal condition, 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]

  1. 25 J
  2. 30 J
  3. −30 J
  4. 5 kJ
NEET (UG) 2019
9

The bond dissociation energies of X2, Y2 and XY are in the ratio of 1 : 0.5 : 1. H for the formation of XY is -200 kJ mol-1. The bond dissociation energy of X2 will be

  1. 800 kJ mol-1
  2. 200 kJ mol-1
  3. 400 kJ mol-1
  4. 100 kJ mol-1
NEET 2018
10

For a given reaction, H = 35.5 kJ mol-1 and S = 83.6 J K-1 mol-1. The reaction is spontaneous at (Assume that H and S do not vary with temperature.)

  1. T > 425 K
  2. all temperatures
  3. T > 298 K
  4. T < 425 K
NEET 2017
11

A gas is allowed to expand in a well insulated container against a constant external pressure of 2.5 atm from an initial volume of 2.50 L to a final volume of 4.50 L. The change in internal energy U of the gas in joules will be

  1. -500 J
  2. -505 J
  3. +505 J
  4. 1136.25 J
NEET 2017

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