🔥 Thermodynamics (Chapter–11)
Complete Notes for Students
1. Thermal Equilibrium & Temperature
Two bodies are in thermal equilibrium if no heat flows between them.
Temperature is the physical quantity that determines the direction of heat flow.
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2. Zeroth Law of Thermodynamics
If two systems are separately in equilibrium with a third system, then they are in equilibrium with each other.
This law helps define temperature.
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3. Heat, Work and Internal Energy
- Heat (Q): Energy transfer due to temperature difference
- Work (W): Energy transfer when force causes displacement
- Internal Energy (U): Total energy of molecules
4. First Law of Thermodynamics
ΔU = Q − W
- Q = Heat supplied
- W = Work done by system
5. Second Law of Thermodynamics
- Heat cannot flow from cold to hot body without external work
- No engine is 100% efficient
6. Thermodynamic Variables
- Pressure (P)
- Volume (V)
- Temperature (T)
Equation of State
PV = nRT
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7. Thermodynamic Processes
(A) Isothermal Process
Temperature constant (T = constant)
PV = constant
PV = constant
(B) Adiabatic Process
No heat exchange (Q = 0)
PVᵞ = constant
PVᵞ = constant
(C) Isobaric Process
Pressure constant (P = constant)
(D) Isochoric Process
Volume constant (V = constant)
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8. Reversible and Irreversible Processes
- Reversible: Can be reversed without energy loss
- Irreversible: Cannot be reversed completely
9. Cyclic Process
System returns to initial state.
Net change in internal energy = 0
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10. Important Points
- Zeroth law defines temperature
- First law is conservation of energy
- Second law defines direction of processes
- Adiabatic process has no heat exchange
- Cyclic process has zero change in internal energy
