Introduction

Thermodynamics is the science of the relationship between heat , work and the properties of the systems. More recently Thermodynamics has been defined as the science of energy and its relation to matter. Thermodynamics is based on the laws of Thermodynamics referred to as the ,

• Zeroth law
• First law
• Second law 
• Third law

These laws result from our experiences of the world of inanimate matter. They are accepted as laws of of nature because they have not been violated even in single instance. Based on these laws , methods of Thermodynamic analysis have been built up by the use of logic and mathematics.

By means of these methods we are able to predict the behavior of Engines , Refrigerators , and other fluid handling machinery , and of matter subjected to chemical reactions , electrical and magnetic processes or other transactions which affect energy.

Thermodynamic systems

matter:

The physical world is made of matter. If we take what is called a microscopic view , we find that matter is made up of atoms or , in many cases , identifiable groups of atoms , which are called molecules. A subdivision of matter into smaller and smaller parts brings us progressively to , molecules and atoms ; protons , neutrons and electrons.

The energy possessed by a given piece of matter can in the final analysis be associated with its micro structure , i.e. the arrangement of and the inter-relationships between the subdivisions of matter. For example , a mass of gas will have energy by way of the Kinetic energy of molecules which are in random motion. The stretching of a rubber band causes the long-chain molecules which are random motion.  The stretching of a rubber band causes the long-chain molecules in it to change their shape; this strains the bonds between atoms which form the molecules. Here we find storage in the form of Strain energy. The linkage of atoms in a molecule or in a crystal brings about the straining of valency bonds , and this is the manner in which Chemical energy is stored. The electrons which go around the nucleus of an atom have energy by virtue of their linear velocity and of spin about their own axes. The nucleus can spin about its axis and thus have Rotational kinetic energy. Within the nucleus the protons and neutrons being held close to each other results in the storage of energy. This is called Binding energy. Relativistic  mechanics tells us that matter and energy are interchangeable. Even though matter and energy are associated with each other in a discrete manner on a microscopic level , the subject of thermodynamics deals with matter in the form of continuum. In order to see matter as a continuum , we take what is called a macroscopic view. A macroscopic view does not get us involved with the velocities and energies of individual particles ; we can describe matter in terms of statistically derived quantities which cannot be associated with single particles , but are meaningful only in relation to groups.

System: 

A thermodynamic system consists of matter which we can identify. Identification requires that the matter , irrespective of the phase or mixture of phases obtaining in it , remains within an identifiable  and continuous boundary. The System boundary  will enclose all the matter associated with the system and leave out all that which is not a part of the system. This boundary may be real or imaginary , and all matter outside boundary forms the surroundings or the environment.

Closed system:

A system is referred to as an open system when no matter crosses its boundary. Thus the matter enclosed by the system boundary remains the same throughout.

Open system: 

If matter flow pass the boundary , the system is referred to as an Open system. Here we are able to identify the matter entering and leaving the system during any period and also the matter present within the boundary at any time. there may be more than one incoming stream and more than one out going stream through which matter enters and leaves. The streams may be steady or non-steady.

In thermodynamics and fluid mechanics , the system boundary , especially that of an open system , is also referred to as the control surface. The enclosed space is referred to as the control volume , we can write the continuity equation.

Property:

To have a complete knowledge of a system at a given instant in a thermodynamic sense we must know its  properties. Each property can be assigned a numerical value. The values of the properties will not tell us anything about the history of the system. Volume , mass , pressure , temperature , energy , magnetization , and polarization , are of some of the properties which may be interest to us. Particularly , volume , temperature , and pressure are properties which only thermodynamics systems can have ; individual atoms, molecules and sub-atomic particles do not have these properties. 

We can classify properties into two groups ,

• Intensive
• Extensive

 Intensive properties can be defined at a point or locality within a system , and extensive properties refer to the system as a whole so that they depend on the extent of the system.   

State of a system:            

The state of a system is fixed by all of its properties. 

state = f ( all properties)

The thermodynamic ' state ' must not be confused with the ' phase ' of a substance.

Internal equilibrium:

If there are no local variations of properties within a closed system at a given instance , then we say that it is in internal equilibrium. If the closed system is kept in isolation for a sufficiently long time , local variations in its properties can be made as small as we like.( When a closed system is isolated in such a way that the surroundings cannot influence it at all , it is said to be isolated.)

Process:

A process is an action that makes a system change from one state to another. the cyclic process is a special kind of process is in which the starting and the finishing states are identical.