Definition of Thermodynamic Terms and Types of System

Definition of Thermodynamic Terms and Types of System

Introduction to Thermodynamics
  • Thermodynamics is formed by combination of two Greek words – ‘therme‘ and ‘dynamikos‘.
  • The word ‘therme’ means “heat” and ‘dynamikos’ stands for “power or motion”.
    i.e., the flow of heat is called thermodynamics

Definition of Thermodynamics
The branch of physical chemistry that deals with the study of heat, temperature and their relation to energy and work is called as thermodynamics.
It is concerned with the laws governing the exchange of heat and transformation of energy from one form to another.

Example
The laws of thermodynamics govern the working of refrigerators, heating and air conditioning systems, pressure cookers, water heaters, humidifiers etc.
Also the design and analysis of rockets, jet engines, solar collectors, cars, airplanes, power plants etc. is based on the laws of thermodynamics.

Experiment :-
Rubbing hands (the mechanical energy converting into heat energy)
Steam engines ( heat energy converts into mechanical energy)

Limitations of Thermodynamics
1. The law of thermodynamics apply only to the matter in bulk (i.e., macroscopic system) and not to the individual atoms or molecules of the macroscopic system.

2. Thermodynamics can only predict feasibility or spontaneity of a process under a given set of conditions but does not tell anything about the rate at which the given process may proceed.

3. It is not concerned with the total energy of the body but only with energy change.

Definition of Thermodynamic Terms :-

System
The part of universe which is under observation or consideration is called as system.

Surrounding
The rest part of universe other than system is called as surrounding.
i.e., the system and surrounding together constitute the universe or
The Universe = System + Surrounding

  • We are never interested in the surrounding.
  • Our study is only restricted to the system.

Boundary
Anything which separates the system and surrounding is called as boundary.
The boundary may be real or imaginary, rigid or non rigid, conductor or non-conductor.

Example of system, surrounding and boundary :-
When a reaction is carried out in a beaker then the contents of beaker constitute the system, beaker serves as boundary and anything which is outside the beaker is called surrounding.

Types of System

System can be classified in two ways :
1. On the basis of exchange of energy and matter
2. On the basis of composition

1. On the basis of exchange of energy and matter
(a) Open System
This type of system can exchange energy as well as matter with the surrounding.
For example – the presence of reactants in an open beaker.

(b) Closed System
This type of system can exchange energy with its surrounding but there is no exchange of matter in a closed system.
For example – the presence of reactants in a closed vessel made up of conducting material e.g. copper, steel etc.

(c) Isolated System
In an isolated system, there is no exchange of energy or matter with the surrounding.
For example – the presence of reactants in a thermos flask or any other closed insulated vessel.

Note:-
In an open system, the boundary is not sealed and not insulted.
In a closed system, the boundary between the system and surrounding is sealed but not insulted.
Isolated systems are perfectly insulated systems and can not interact in any way with its surrounding.

2. On the basis of composition
(a) Homogeneous System
A system is said to be homogeneous when it is completely uniform throughout the bulk i.e.,
a homogeneous system is made of one phase only.
For example – a pure single solid, liquid , gas, mixture of gases.

(b) Heterogeneous System
A system is said to be heterogeneous when it is not uniform throughout i.e.,
it consists of two or more phases.
For example – ice in contact with water, insoluble solids in contact with a liquid.

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