# CBSE Class 11th Physics Notes for Chapter 12 Thermodynamics

Chapter 12 Thermodynamics

ZEROTH LAW OF THERMODYNAMICS

This law states that ‘two systems in thermal equilibrium with a third system are in thermal equilibrium with each other.

THE FIRST LAW OF THERMODYNAMICS

It is the general law of conservation energy applied to any system in which energy transfer from or to the surroundings (through heat and work) is taken into account.

THE SECOND LAW OF THERMODYNAMICS

It states:

Kelvin-Planck statement: No process is possible whose sole result is the absorption of heat from a reservoir and complete conversion of heat into work.

Clausius statement: No process is possible whose sole result is the transfer of heat from a colder object to a hotter object.

It implies that no heat engine can have efficiency equal to 1 or no refrigerator can have co-efficient of performance equal to infinity.

A process is reversible if it can be reversed such that both the system and the surroundings return to their original states, with no change anywhere else in the universe. Spontaneous processes of nature are irreversible.

CARNOT’S ENGINE

Carnot’s engine is a reversible engine operating between two temperatures T1 (source) and T2 (sink). The Carnot cycle consists of two isothermal processes connected by two adiabatic processes.

No engine operating between two temperatures can have efficiency greater than that of a Carnot engine.

If Q > 0, heat is added to the system

If Q < 0, heat is removed from the system

If W > 0, work is done by the system

If W < 0, work is done by the system