🔥 Thermodynamics – Objective Page 9

IIT Advanced PYQ Thinking • Assertion Logic • Deep Concepts

✔ Questions where equations FAIL
✔ Laws + logic = answer
✔ Designed to break average students

🧠 Concept 1: Entropy without Formula

If a process:

Occurs naturally → ΔS_universe ≥ 0
Needs external intervention → ΔS_universe < 0

IIT Trick: Check “natural or forced” first.

🧠 Concept 2: Reversible vs Irreversible Trap

Reversible process:

Infinitely slow
No entropy generation

Trap: Fast ≠ reversible even if frictionless.

🧠 Concept 3: Work–Heat Confusion

Heat = path dependent
Work = path dependent
Internal energy = state function

PYQ Pattern: Same initial & final state → ΔU same.

🧠 Concept 4: Free Expansion Logic

For ideal gas free expansion:

Q = 0
W = 0
ΔU = 0

Result: Temperature unchanged.

🧠 Concept 5: Carnot Engine Reasoning

If two engines operate between same reservoirs:

Maximum efficiency = Carnot
Efficiency independent of working substance

Assertion–Reason Favorite

🧠 Concept 6: Refrigerator vs Engine

Engine → produces work
Refrigerator → consumes work

PYQ Twist: Direction of heat flow decides device type.

🧠 Concept 7: Entropy of Isolated System

For isolated system:

Entropy never decreases
Maximum at equilibrium

Gold Rule: Nature moves toward maximum entropy.

🧠 Concept 8: Mixing of Gases

Mixing of ideal gases:

ΔU = 0
ΔT = 0
ΔS > 0

Entropy always increases.

🧠 Concept 9: PV Diagram Mastery

Area under curve = work
Steeper curve ≠ more work always

Compare areas, not slopes.

🧠 Concept 10: Elimination Master Trick

If any option:

Violates First Law → Reject
Violates Second Law → Reject

Even before solving numerically.

✅ Objective Page 9 Completed
➡ Next: Page 10 – Ultimate IIT Advanced Mixed Problems

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🔥 Thermodynamics – Objective Final Revision

Thermodynamics – Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 10
Set 11
Set 12
Set 13
Set 14
Set 15
Set 16
Set 17
Set 18
Set 19
Set 20
Set 21
Set 22
Set 23
Set 24
Set 25
Set 26
Set 27
Set 28
Set 29
Set 30
Set 31
Set 32
Set 33
Set 34
Set 35
Set 36
Set 37
Set 38
Set 39
Set 40
Set 41
Set 42
Set 43
Set 44
Set 45
Set 46
Set 47
Set 48
Set 49
Set 50
Set 51
Set 52
Set 53
Set 54
Set 55
Set 56
Set 57
Set 59

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