There are following types of processes :
(1) Isothermal process : It is defined as a process in which the temperature of the system remains constant throughout the change of a state of the system.
In this,
ΔT = 0.
Features :
- In this process, the temperature at initial state, final state and throughout the process remains constant.
- In this process, system exchanges heat energy with its surroundings to maintain constant temperature. E.g., in case of exothermic process liberated heat is given to the surroundings and in case of endothermic process heat is absorbed from the surroundings so that temperature of the system remains constant and ΔT = 0.
- Isothermal process is carried out with a closed system.
- Internal energy (U) of the system remains constant, hence, Δ U = 0.
- In this process, pressure and volume of a gaseous system change.
(2) Isobaric process : It is defined as a process which is carried out at constant pressure. Hence, Δ P = 0.
Features :
- In this process, the volume (of gaseous system) changes against a constant pressure.
- Since the external atmospheric pressure remains always constant, all the processes carried out in open vessels, or in the laboratory are isobaric processes.
- In this volume and temperature change.
- Internal energy of a system changes, hence, ΔU ≠ 0.
(3) Isochoric process : It is defined as a process which is carried out at constant volume of the system.
Features :
- In this process, temperature and pressure of the system change but volume remains constant.
- Since ΔV = 0, no mechanical work is performed.
- In this internal energy (U) of the system changes. The example of this process in cooking takes place in a pressure cooker.
(4) Adiabatic process : It is defined as a process in which there is no exchange of heat energy between the system and its surroundings. Hence, Q = 0.
Features :
- An adiabatic process is carried out in an isolated system.
- In this process, temperature and internal energy of a system change, ΔT ≠ 0, Δ U ≠ 0.
- During expansion, temperature and energy decrease and during compression,temperature and energy increase.
- If the process is exothermic, the temperature rises and if the process is endothermic the temperature decreases in the adiabatic process.
(5) Reversible process : A process carried out in such a manner that at every stage, the driving force is only infinitesimally greater than the opposing force and it can be reversed by an infinitesimal increase in force and the system exists in equilibrium with its surroundings throughout, is called a reversible process.
Features :
- This is a hypothetical process.
- Driving force is infinitesimally greater than the opposing force throughout the change.
- The process can be reversed at any point by making infinitesimal changes in the conditions.
- The process takes place infinitesimally slowly involving infinite number of steps.
- At the end of every step of the process, the system attains mechanical equilibrium, hence, throughout the process, the system exists in temperature-pressure equilibrium with its surroundings.
- In this process, maximum work is obtained.
- Temperature remains constant throughout the isothermal reversible process.
(6) Irreversible process : it is defined as the unidirectional process which proceeds in a definite direction and cannot be reversed at any stage and in which driving force and opposing force differ in a large magnitude. It is also called a spontaneous process.
Features :
- It takes place without the aid of external agency.
- All irreversible processes are spontaneous.
- All natural processes are irreversible processes.
- Equilibrium is attained at the end of process.
- They are real processes and are not hypothetical.
Examples :
- Flow of heat from a matter at higher temperature to a matter at lower temperature.
- Flow of a gas from higher to lower pressure.
- Flow of water from higher level to lower level.
- Flow of a solvent into a solution through a semipermeable membrane due to osmosis.
- Flow of electricity from higher potential terminal to lower potential terminal.
