Basic Concepts of Thermodynamics

Topics: Thermodynamics, Temperature, Energy Pages: 9 (2753 words) Published: October 16, 2010

Basic Concept and Definition
Thermodynamics is known as a branch of the physics and also conceptualise engineering science. Scientists are normally interested in understanding fundamentals of physical as well as chemical behavior of the fixed and the quiescent quantities of matter and also use principles of the thermodynamics to relate properties of the matter. Whereas, engineers are in general interested in studying the systems and their interaction with the surroundings. In order to facilitate this, engineers extended the study of thermodynamics to study of the systems through which the matter flows. Systems

In thermodynamic analysis, the system is known as a specified quantity of the matter and the region which can be parted off from its surrounding by a well-defined system boundary. The surface boundary can be fixed or movable. Everything which is outside to system is known as surroundings. A system which has fixed mass is known as closed system. Whereas a system is called an open system if mass flows through its system boundary. An isolated system is also a closed system which is not interacting with its surrounding any ways. State, Property

Condition of the system at any particular instant of time is known as state of the system. Properties of a system are given by state of the system at that given instant of the time. A property is a quantity or a set of quantities, of those numerical values which depends on state of the system, not its history. Value of these properties can be determined by some physical operations or tests. Extensive properties are those which depend on size of a system. A few examples of the extensive properties are Volume, mass, energy, and entropy. The value of an extensive property for the whole system is additive i.e. equals to the sum of values of its parts. An Intensive property is independent of size of a system. A few examples of intensive properties are the pressure and the temperature. A mole is a quantity of the substance whose mass is equal to the molecular weight of that substance. If a molecular weight of a substance is M and number of the moles are n, then mass m of that substance is m = n X M. One kilogram mole (kmol) of the oxygen is equals to 32.0 kg. If an extensive property is calculated on the basis of the unit mass or the unit mole, it is known as a specific property.

Process and Cycle
Two states of a system are known to be identical if, and only if, properties of both the states are identical in nature. If the value of the property of the system gets changed, it is called as a change in the state. This phenomenon of the system is known as a process. A system at a given initial state after going through a sequence of various processes returns to the same initial state, it is called as a cycle. Phase and a pure substance

Phase is a quantity of matter which remains homogeneous throughout in the chemical composition and the physical structure both. If a matter is all solid, or all liquid, or all vapour (or all gas), it is called homogeneous in their physical structure. A system may contain one phase or more than one phase. As an example, a system of the liquid water and the steam (water vapour) has two phases. If the chemical composition of a substance is uniform and invariable, it is called as pure substance. Pure substance may exist in more phases, however, the chemical composition of that substance must be same in all its phases. As an example, if water (liquid) and steam (vapour) make a system that has two phases, that system may be called as pure substance because both the phases has same chemical composition.

Equilibrium means balance condition. In thermodynamics this concept includes balance of the forces and a balance of the other influences as well. These influences may be particular aspect of the thermodynamic equilibrium. Thermal equilibrium means an equality of the temperature; mechanical equilibrium means an equality of the...
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