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Consider a system of gas exists in a cylinder. The piston consists of many very small pieces of weights. Initially system is in an equilibrium state. When the gas system is isolated, the weights on piston are removed one by one slowly, at any instant of upward travel of the piston. So every state passes through by the system will be in an equilibrium state. Thus the system passes through the locus of all equilibrium points. This infinitely slow system is a quasi-static process. If the same small weights are now placed slowly one by one on top of the piston then the process will reverse in the same manner. When a process is processing in such a way that system will be remained infinitesimally close with equilibrium state at each time, such process will be termed as quasi static process or quasi equilibrium process. In simple words, we can say that if system is going under a thermodynamic process through succession of thermodynamic states and each state is equilibrium state th

The two systems are said to be in thermodynamic equilibrium with each other when they are in mechanical, chemical and thermal equilibrium with each other. Here are various types of equilibrium and the conditions for thermodynamic equilibrium of the system. Thermodynamic Equilibrium Defined Let us suppose that there are two bodies at different temperatures, one hot and one cold. When these two bodies are brought in physical contact with each other, temperature of both the bodies will change. The hot body will tend to become colder while the cold body will tend to become hotter. Eventually both the bodies will achieve the same temperatures and they are said to be in thermodynamic equilibrium with each other. In an isolated system when there is no change in the macroscopic property of the system like entropy, internal energy etc, it is said to be in thermodynamic equilibrium. The state of the system which is in thermodynamic equilibrium is determined by intensive properties such a

Homogeneous and heterogeneous thermodynamic systems A  homogeneous thermodynamic system  is defined as the one whose chemical composition and physical properties are the same in all parts of the system, or change continuously from one point to another. A homogeneous system can be exemplified by imagining a column of atmospheric air, which is a mixture of a number of gases, mainly nitrogen and oxygen. In a system of this kind, acted upon by the force of gravity, both the composition of the system and its physical properties will continuously change from one point to another. A  heterogeneous system  is denned as one consisting of two or more homogeneous bodies. The homogeneous bodies of a heterogeneous system are referred to as  phases.  Each phase is separated from other phases by interfaces, or boundaries, and in passing over such a boundary the chemical composition of the substance or its physical properties abruptly change. This phase boundary must not be regarded as a math

The term thermodynamic system infers the definite amount of matter that is subjected to thermodynamic analysis. The system is defined by a boundary line beyond which it is referred as surrounding. For a thermodynamic system, mass is fixed and the boundary changes with time. Control volume is the amount of matter and space bounded by the control surface which is the imaginary boundary (window) along the passage of the considered matter. For control volume, mass varies with time and  boundary (control surface) is fixed. 1. SYSTEM,BOUNDARY, SURROUNDINGS System -A thermodynamics system is defined a definite space or area on which the study of Energy Transfer and Energy conversions is made Boundary –The system and surrounding are separated by boundary. It may be fixed or movable or imaginary.It will not occupy any volume or mass in space 2.  Surroundings - Anything outside the system which affects the behaviour of the system is known as surroundings Control volume – A specifi

Macro simply means big or large and micro refers to nano,small or tiny thus viewpoints refers to the perceptive through which an observer witnesses it's surrounding,this term is totally relative as an example:- The planet earth is extremely big as compared to a some stone on a beach but it is extremely small as compared to the sun thus for an observer the macro and micro viewpoints changes with relativity. Macroscopic Approach: In this approach a certain quantity of matter is considered without taking into account the events occurring at molecular level. In other words this approach to thermodynamics is concerned with gross or overall behaviour. This is known as classical thermodynamics. The analysis of macroscopic system requires simple mathematical formula. The value of the properties of the system are their average values. For examples consider a sample of gas in a closed container. The pressure of the gas is the average value of the pressure exerted by millions