🔥 Thermodynamics – Stage 1

Page 2 : Heat, Work & P–V Diagrams (JEE Core)

Core Idea:
Energy transfer in thermodynamics happens only in two ways: Heat (Q) and Work (W).

1️⃣ Heat (Q)

Heat is the form of energy transferred due to temperature difference between the system and surroundings.

Key Points:
• Heat flows from higher to lower temperature
• Heat is a path function
• Heat is NOT stored in a system

❌ System does NOT possess heat ✔ System possesses internal energy

2️⃣ Work (W)

Work is said to be done when a force causes displacement at the boundary of the system.

In Thermodynamics:
Work is mainly associated with change in volume.

3️⃣ Work Done in Volume Change

For a gas inside a cylinder:

Infinitesimal Work:
dW = P dV

Total Work:
W = ∫ P dV

➤ Area under P–V curve = Work done

4️⃣ Sign Convention (VERY IMPORTANT)

Work Done:
• Expansion → W positive
• Compression → W negative

Heat Transfer:
• Heat absorbed → Q positive
• Heat released → Q negative

5️⃣ Pressure–Volume (P–V) Diagram

A P–V diagram is a graphical representation of thermodynamic processes.

Axes:
• X-axis → Volume (V)
• Y-axis → Pressure (P)

6️⃣ Important Thermodynamic Processes

(a) Isobaric Process (P = constant)
• Horizontal line on P–V diagram
• Work = P(V₂ − V₁)

(b) Isochoric Process (V = constant)
• Vertical line on P–V diagram
• Work = 0

(c) Isothermal Process (T = constant)
• Hyperbola on P–V diagram
• PV = constant

(d) Adiabatic Process (Q = 0)
• Steeper curve than isothermal
• PV^γ = constant

7️⃣ Zero Work Situations

Work = 0 when:
• No change in volume
• Free expansion in vacuum
• Rigid container

📌 JEE Exam Traps

• Area under curve ≠ area between curves
• Vertical line → zero work
• Work depends on path, not just end states
• Same ΔV ≠ same work (path matters)

👉 Next Page:
Page 3 – First Law of Thermodynamics (ΔQ = ΔU + W)

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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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