# LAW OF THERMODYNAMICS

Thermodynamics is the study which deals with energy the various concepts and laws describing the conversion of one from of energy to another , and the various systems employed to effect the conversions .Thermodynamics deals in general with system in equilibrium .By means of its fundamental concepts and basic laws the behaviour of an engineering system may be described when the various variables are altered . The quantity of matter under consideration is called the system and everything else is spoken of as surrounding . With an closed system  there is no interchange of matter between system and surroundings . With an open system there is such interchange  Any change that the system may undergo is known as a process . Any process or series of processes in which the system returns of its original condition or state is called a cycle .

## Zeroth law of thermodynamics

When a body A is in thermal equilibrium with a body B & also separately with a body C then body B & C will be in thermal equilibrium with each other .

{ Zeroth law of thermodynamics is the basic of temperature measurement }

### The First law of thermodynamics

The first law of thermodynamics is a rigorous statement of the principle of conversion of energy . This law has been stated in a variety of ways , some of the typical statements are :
(1) Whenever energy is transformed from one from to another , energy is always conserved .
(2) Energy can neither be created nor destroyed .
(3) The sum total of all energy remains constant .

OR
It is observed that when a system is made to undergo a complete cycle then net work is done on or by the system . consider a cycle in which net work is done by the system . Since energy cannot be created .this mechanical energy must have been supplied from source of energy . Now the system has been returned to its initial state : Therefore : its intrinsic energy is unchanged , and hence the mechanical energy has not been provided by the system itself .The only other energy involved in the cycle is the heat which was supplied and rejected in various processes . Hence by the law of conservation of energy , the net work done by the system is equal to the net heat supplied in the system .The First law of thermodynamics  can , therefore be stated as follows ;
" When a system undergoes a thermodynamics cycle then the net heat supplied to system from the surrounding is equal to net work done by the system on its surroundings ".
The First law of  thermodynamics  may also be stated as follows .
" Heat and work are mutually convertible but since energy can neither be created nor destroyed , the total energy associated with an energy conversion remains constant " .

Application of First law of process

When a process is executed by a system , the change in started energy of the system is numerically equal to the net heat interactions minus the net work interaction during the process .

When E represents the total internal energy .
IF the electric magnetic and chemical energies are absent and and changes in potential and Kinetic energy for a closed system are neglected the above equation can be written as

The First law of thermodynamics

### The second law of thermodynamics

The second law of thermodynamics states that conversion of heat to work is limited by the temperature at which conversion at which conversion occurs . it may be be shown that .

1. No cycle can be more efficient than reversible cycles operating between given temperature limits .

2. The efficiency of all reversible cycles absorbing heat only at a single constant higher temperature T 1 and rejecting heat only at a single constant lower temperature T 2 must be the same .

3. For all such cycles the efficiency is
T 1 - T 2
Efficiency =-------------
T 2

This is usually called the Carnot cycle efficiency .

OR

The second law of thermodynamics
Kelvin -Plank statement
It is impossible for a heat engine to produce net work in a complete cycle if it exchanges heat only with bodies at a single fixed temperature .
Two reversible adiabatic paths cannot intersect each other which violates the kelvin- Plank statement .
The machine which violate kelvin - Plank statement  is called PMM2 .

Clausius Statement
Is impossible to construct a device which operating in a cycle transfer heat from cooler body to a hotter body without any work input .

The second law of thermodynamics

### The third law of thermodynamics

Introduce the concept of absolute entropy . It states that the total entropy of pure substance approaches zero as the absolute thermodynamics temperature approaches zero . The third law implies further that the partial derivatives with respect to temperature of generalized force and generalized displacement also vanish at absolute zero .