Thermodynamics – Notes

Thermal equilibrium and Zeroth law
Thermodynamics is the study of “exchange of ‘heat’ and ‘work’ between a system and its surrounding “, and the “resultant changes in the macroscopic variables of the said system”.
A thermodynamic system is an isolated body or a group of bodies with a well defined boundary.
The state of a system changes:
1. If the system exchanges heat with its surroundings.
2. When ‘work’ is done by the system or on the system.
An adiabatic wall does not allow any flow of heat through it where as diathermic wall allows flow of heat through it.
Two systems ‘A’ and ‘B’ are said to be in “thermal equilibrium”, when they are in contact with each other or separated by a diathermic wall and the system A is in equilibrium with the state of system B.
When two systems, ‘A’ and ‘B’ are individually in thermal equilibrium with a third system ‘C’, they are in thermal equilibrium with each other.
This is known as “Zeroth law of Thermodynamics”.

Heat, internal energy and work
Temperature is a thermodynamic variable that is equal for system in thermal equilibrium.