Complete Thermodynamics Notes (NEET)

1. Basic Concepts

Concepts

Thermodynamics deals with macroscopic systems.
Focus on heat, work and energy.

Heat (Q)

Energy in transit
Flows due to temperature difference
Not stored energy

Work (W)

Energy transfer due to force/displacement.

Internal Energy (U)

Total microscopic energy (KE + PE of molecules)

Quantity	Type
Heat	Path function
Work	Path function
Internal Energy	State function

2. Zeroth Law

Explanation

If A is in equilibrium with B and B with C → A with C.

Defines temperature

Trap: Students confuse with energy ❌

3. First Law

Formula + Meaning

Q = ΔU + W

Case	Sign
Heat supplied	+Q
Work by system	+W
Work on system	-W

Energy is conserved.

4. Thermodynamic Processes

All Processes

Isothermal

T constant
ΔU = 0
Q = W

Adiabatic

Q = 0
ΔU = -W
Expansion → cooling
Compression → heating

Isochoric

Volume constant
W = 0
Q = ΔU

Isobaric

Pressure constant
W = PΔV

5. Heat Capacity

Details

C = Q / ΔT

Cp → constant pressure
Cv → constant volume

Cp > Cv

6. Second Law

Statements

Kelvin-Planck

100% heat → work impossible

Clausius

Heat flows hot → cold

Reverse needs work

7. Reversible vs Irreversible

Comparison

Type	Features
Reversible	Infinitely slow, no loss
Irreversible	Real, energy loss

8. Carnot Engine

Concept + Formula

Ideal engine with max efficiency

η = 1 - (T₂ / T₁)

Temperature must be in Kelvin
Independent of gas
Efficiency less than 100%

9. NEET Traps

Must Revise

Heat ≠ internal energy
ΔU = 0 → isothermal
Q = 0 → adiabatic
W = 0 → isochoric
Cp > Cv
100% efficiency impossible
Heat flows hot → cold
Reversible = infinitely slow
Adiabatic expansion cools gas

10. Exam Strategy

How to Solve Questions

Identify process first
Apply correct relation
Check sign convention
Use Kelvin in Carnot