🔥 Thermodynamics – Stage 1

Page 7 : First Law of Thermodynamics (JEE Core)

Core Law:
Energy can neither be created nor destroyed, only transformed

1️⃣ Mathematical Statement of First Law

ΔQ = ΔU + W

ΔQ → Heat supplied to system
ΔU → Change in internal energy
W → Work done by system

⚠ Sign Convention (Very Important):
Heat given to system → +ΔQ
Work done by system → +W

2️⃣ Internal Energy (ΔU)

Internal energy depends only on temperature for an ideal gas.

For Ideal Gas:
ΔU = nC_vΔT

• Path independent quantity
• Same initial & final temperature → same ΔU

3️⃣ First Law for Important Processes

(a) Isochoric Process (V = constant)

W = 0
ΔQ = ΔU

Heat supplied → Fully increases internal energy

(b) Isobaric Process (P = constant)

W = PΔV
ΔQ = ΔU + PΔV

(c) Isothermal Process (T = constant)

ΔU = 0

ΔQ = W

All heat supplied converts into work

(d) Adiabatic Process (Q = 0)

ΔQ = 0

ΔU = −W

Work done → Comes from internal energy

4️⃣ First Law in Cyclic Process

For a complete cycle:
ΔU = 0

Therefore:
ΔQ = W

Net heat absorbed = Net work done

5️⃣ JEE-Trap Table

Process	ΔQ	ΔU	W
Isochoric	≠ 0	≠ 0	0
Isothermal	≠ 0	0	≠ 0
Adiabatic	0	≠ 0	≠ 0
Cyclic	≠ 0	0	≠ 0

6️⃣ Advanced Problem-Solving Tips

• First identify process type
• Decide zero quantity first (ΔQ, ΔU, or W)
• Apply ΔQ = ΔU + W
• In cycles, forget ΔU completely

👉 Next Page:
Page 8 – Heat Capacities (C_p, C_v, Mayer’s Relation)

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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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