Basic concepts
(1) System, surroundings and Boundary : A specified part of the universe which is under observation is called the system and the remaining portion of the universe which is not a part of the system is called the surroundings.
The system and the surroundings are separated by real or imaginary boundaries. The boundary can also be defines the limits of the system. The system and surroundings can interact across the boundary.
(2) Types of systems
(i) Isolated system : This kind of system has no interaction with the surroundings. The boundary of it is sealed and insulated. The matter and energy cannot be exchanged with the surrounding. A substance contained in the ideal thermos flask is an example of the isolated system.
(ii) Closed system : This kind of system can exchange energy in the form of heat, work or the radiations but not matter with its surroundings. The boundary between the system and surroundings is sealed but not insulated. For instance, liquid in contact with vapour in the sealed tube and pressure cooker.
(iii) Open system : This type of system can exchange matter as well as energy with its surroundings. The boundary is neither sealed nor insulated. Sodium reacting with water in an open beaker is an example of open system.
(iv) Homogeneous system : A system is said to be homogeneous when it is completely uniform throughout. The homogeneous system is made up of one phase only. Such as a pure liquid or gas, single solid, mixture of gases and a true solution.
(v) Heterogeneous system : A system is said to be heterogeneous when it is not uniform throughout, that is it consist of two or more phases. Examples : ice in contact with the water, two or more immiscible liquids which are insoluble solid in contact with a liquid, a liquid in contact with vapourand many more
(vi) Macroscopic system : The macroscopic system is one in which there are a large number of particles (might be atoms, molecules, ions etc. )
(3) Macroscopic properties of the system deals with matter in terms of bulk (large number of chemical species) behavior. The properties of the system which arise from the bulk behavior of matter are called macroscopic properties. The general examples of the macroscopic properties are refractive index, volume, temperature, surface tension, pressure, viscosity, density, etc.
The macroscopic properties can be subdivided into two types,
(i) Intensive properties : The properties which do not depend upon the quantity of matter present in the system or size of the system are called intensive properties. Its examples are temperature, refractive index, pressure, density, specific heat, boiling point, viscosity, melting point, volume per mole, surface tension, concentration etc.
(ii) Extensive properties : The properties whose magnitude depends upon the quantity of matter present in the system are called extensive properties. Its examples are total mass, volume, internal enthalpy, entropy energy, etc. The above stated properties are additive in their nature.
Any of the extensive property if expressed as per the mole or per gram becomes an intensive property.
(4) The state of a system and the State of Variables
Macroscopic properties which determine the state of a system are referred to as state variables or state functions or thermodynamic parameters. The change in state properties depends upon the initial and final states of the system only, but it is independent of the manner in which the change has been brought about. Or we can say that the state properties do not depend upon a path followed.
(5) Thermodynamic equilibrium : A system is said to have attained a state of thermodynamic equilibrium when it shows no further tendency to change its property with time.
The principle for thermodynamic equilibrium needs that the following three types of the equilibrium exist simultaneously in the system,
(i) Chemical Equilibrium : A system in which the composition of the system remains fixed and definite.
(ii) Mechanical Equilibrium : No chemical work is done between different parts of the system or between the system and surrounding. It can be attained by keeping pressure constant.
(iii) Thermal Equilibrium : The temperature remains constant which means no flow of heat between system and surrounding.
(6) Thermodynamic process : When thermodynamic system changes from one state to the other, the operation is known as process. The various types of the processes are written as follows
(i) Isothermal process : In this process operation is done at the constant temperature dT = 0 thus ΔE = 0.
(ii) Adiabatic process : In this a process there is no exchange of heat takes place between the system and surroundings. The system is thermally isolated, i.e., dQ = 0 and its boundaries are insulated.
(iii) Isobaric process : In this process the pressure remains constant throughout the change i.e., dP = 0.
(iv) Isochoric process : In this process volume remains constant throughout the change, i.e., dV = 0.
(v) Cyclic process : When a system undergoes a number of different processes and finally return to its initial state, it is called as cyclic process. For the cyclic process dE = 0 and dH = 0.
(vi) The reversible process : The process which occurs infinitesimally slowly, that is opposing force is infinitesimally smaller than driving force and when infinitesimal increase in the opposing force can reverse the procedure, it is said to be reversible process.
(vii) Irreversible process : When the process occurs from initial to final state in single step in finite time and cannot be reversed, it is called as irreversible process. The amount of entropy increases in irreversible process.
The Irreversible processes are impulsive in nature. All the natural processes are irreversible in nature
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