Some thermodyanamic terms

The term thermodynamics literally means flow of heat ( therm - heat and dynamics - movement or flow). Presently thermodynamics is considered to deal not only with the relationship between heat and work but also with the interconversion of all forms of energy. Theermodynamics may therefore be defined as " that branch of science which deals with the study of different forms of energy and the quantitative relationship between them." Thermodynamics is based on certain fundamental principles known as laws of thermodynamics. It deals with matter in bulk ( macroscopic systems), i.e, systems having many molecules and is independent of the atomic and molecular structure. But in statistical thermodynamics where the laws of mechanics are applied to the behaviour of individual molecules and then a suitable statistical average is taken. The results obtained from statistical and classical thermodynamics are however, complementary to each other.

Some Thermodynamic Terms

In order to study the laws of thermodynamics, it is essential to understand certain terms quite offenly used in thermodynamics. These terms have definite meanings. Some of the most commonly used terms are given below :

System, boundary and surroundings

The part of the universe under consideration is called a system, on which the effect of certain variables such as temperature and pressure is to be studied. The system is separated from rest of the space by a definite boundary. The real or imaginary surface separating the system from the surroundings is called the boundary.

Region outside the boundary of any system is termed surroundings. Thus, everything outside the system is considered as surroundings.

Homogeneous system and heterogeneous system

When a system is uniform throughout, it is called a homogeneous system. In other words, a system is said to be homogeneous system when it it has the same chemical composition throughout. For example, a mixture of gases, a pure single liquid or solid or atrue soliution forms a homogenous system .

A heterogeneous system is one of which consists two or more phases. In other words, it is not uniform throughout. Examples of heterous systems are: ice in contact with water, ice in contact with vapours, etc. Here, ice, water and vapour consitute separate phases.

Types of System:

Depending on the nature of boundary, thermodynamic systems are classified into followindg three classes:

1.Open system:

A system which can exchange matter as well as energy with surroundings is called an open system. Some examples are given below:

i) Evaporation of water from a beaker represents an open system. Here, water vapours ( matter) move into atmosphere and heat ( energy) required is absorbed by water from the surroundings.

ii)In the photosynthesis, plants take up carbon dioxide, water ( matter) and sunlight ( energy) in presence of chlorophyll and prodduce carbohydrates. in this process, oxyzen matter is transferred to the surroundings. Hence, plants consitute an open system.

2.Closed system:

A system which may exchange energy but not matter with surroundings is called a closed system. For example, consider boiling water in a closed metallic vessel in which heat is transferred from he burner ( surroundings) to teh system; steam remains inside the vessel. Thus, matter is not exchanged.

3.Isolated system:

A system which cam=n neither exchange matter nor energy with the surrounding is called an isolated system. For example, some water is taken in asn insulated vessel and put a piecce of asodium metal on it. An exothermoic reaction takes place. Neither hydrogen gas( matter) nor heat (energy) is transferred to the surroundings.