Thermodynamics is a branch of Physics which deals with the conversion of heat energy into mechanical work and vice-versa. A gaseous system is called a thermo dynamical system. The state of the system is represented in terms of pressure (p), volume (V), temperature (T) and heat content (Q) of the gas. These four quantities are called thermo dynamical parameters of the system.
Four thermo dynamical operations
1) Isothermal changes : wherein temperature remains constant. The pressure and volume of a given mass of gas change. Two essential conditions are:
a) Walls of container must be perfectly conducting.
b) Changes must be slow.
2) Adiabatic changes : wherein heat content of a gaseous system remains constant. The pressure and volume of a given mass of gas change with consequent change in temperature. Two essential conditions are:
a) Walls of container must be perfectly insulating.
b) Changes must be sudden.
3) Isobaric changes, wherein pressure is kept constant.
4) Isobaric changes, wherein volume is kept constant.
Zeroth law of Thermodynamics
It represents the concept of temperature/thermal equilibrium of a system. According to this law, if two systems A and B are separately in thermal equilibrium with a third system c, then A and B also be in thermal equilibrium with each other.
First law of Thermodynamics
It is basically the law of conservation of energy. According to this law, when certain amount of heat energy (dQ) disappears, an equivalent amount of energy appears in some other form. If (dU) is small increases in internal energy and (dW) is small amount of external work done by the system in expression, then dQ = dU +dW
Second law of Thermodynamics
It defines the direction of flow of heat. According to Clausius statement, it is impossible for a self acting machine unaided by any external agency, to transfer heat from a body at lower temperature to a body at higher temperature. The heat can be transferred from lower temperature to higher temperature only when some external work is done or energy is supplied to the system,. For example, a refrigerator cools things only when electric energy is supplied to it.