CHAPTER 15 : THERMODYNAMICS
The changes in a system with specific reference to interaction with the surroundings through exchange of
heat energy constitutes study of thermodynamics for the present purpose.
These interactions obey certain laws, which can be distilled from observations and experiments.
The science of thermodynamics is largely phenomenological and as such hardly pays any attention to details
of constitution of a thermodynamical system. Attempts to derive laws of thermodynamics as
consequences of Newton's laws of motion have never been successful though statistical mechanics based on
Newtonian laws incorporates a substantial part of thermodynamics.
The scope of this book permits study of thermodynamics essentially
in terms of empirically defined and measured quantities like Heat
energy (Q), Temperature (T), Pressure (P) and Work (W).
15.1 Zeroth Law
The concept of temperature is made objective by this law and is defined as the state of
thermodynamical system which determines the direction of the flow of heat.
If heat energy is not exchanged between two systems then they are said to be in thermal equilibrium.
"If a system A is in thermal equilibrium with a system B, then they are at the same temperature; if
another system C is also in thermal equilibrium with the system A then B and C are also in thermal equilibrium
with each other and the temperature of each is same as that of the other."
The above statement is the Zeroth Law of thermodynamics.