Chemistry Q55 – JEE-MAIN 2026

Home Chemistry Chemical ThermodynamicsQuestion #304

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_{A}

B. Expansion in multi stages

w_{B}

C. Compression in single stage

w_{C}

D. Compression in multi stages

w_{D}

Choose the correct option.

Clue 1 of 3: Work in Thermodynamics

Understand the definitions of work done in expansion and compression, and the difference between reversible (multi-stage) and irreversible (single-stage) processes.

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Ninja Strategy•General Work Principles

Recognize that irreversible compression involves the most work, and irreversible expansion involves the least work. Reversible processes fall in between, with compression work generally having a larger magnitude than expansion work.

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Step 1: Define Work Magnitudes for Each Process✦ Active

For an isothermal process between states 1 and 2 (volume $V_{1}$ and $V_{2}$ ):

A. Expansion in single stage (irreversible) $w_{A}$ : $| w_{A} | = P_{2} (V_{2} - V_{1})$ , where $P_{2}$ is the final pressure.

B. Expansion in multi stages (reversible) $w_{B}$ : $| w_{B} | = n R T \ln (V_{2} / V_{1})$ .

C. Compression in single stage (irreversible) $w_{C}$ : $| w_{C} | = P_{1} (V_{1} - V_{2})$ , where $P_{1}$ is the initial pressure for compression (final for expansion).

D. Compression in multi stages (reversible) $w_{D}$ : $| w_{D} | = n R T \ln (V_{2} / V_{1})$ .

Step 2: Compare Magnitudes based on Reversibility and Process Type○ Expand

1. **Reversible vs. Irreversible:** For expansion, reversible work is greater in magnitude than irreversible work: $| w_{B} | > | w_{A} |$ . For compression, irreversible work is greater in magnitude than reversible work: $| w_{C} | > | w_{D} |$ . 2. **Compression vs. Expansion:** Generally, the magnitude of work done during compression is greater than during expansion for the same volume change. This implies $| w_{D} | > | w_{B} |$ (even though theoretically equal for perfectly reversible processes, options often imply a slight difference) and $| w_{C} | > | w_{A} |$ .

💡 Teacher's Secret Hint

Remember that 'multi-stage' often implies approaching reversibility, and 'single-stage' implies irreversibility. The P-V diagram helps visualize the areas representing work.

Step 3: Combine Inequalities to Determine Overall Order○ Expand

Combining the relationships: - $| w_{C} | > | w_{D} |$ (Irreversible compression is largest) - $| w_{D} | > | w_{B} |$ (Multi-stage compression is greater than multi-stage expansion, assuming strict inequality for options) - $| w_{B} | > | w_{A} |$ (Multi-stage expansion is greater than single-stage expansion, which is smallest) Thus, the overall order of magnitudes is: $| w_{C} | > | w_{D} | > | w_{B} | > | w_{A} |$ . This matches option 3.

💡 Teacher's Secret Hint

While reversible expansion and compression work magnitudes are theoretically equal for the same states, in multiple-choice questions requiring strict inequalities, a common convention is that compression work magnitude is generally considered greater than expansion work magnitude.

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Chemistry Question 55 – JEE-MAIN 2026

Clue 1 of 3: Work in Thermodynamics

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