Chemqueries: Thermodynamic process

Saturday, 8 December 2018

Thermodynamic process

Thermodynamic process:

        It is the path or operation by which a system changes from one state to another state.

1. Isothermal process:

        The temperature of the system remains constant during each step.
        T = constant => dT = 0


  • For such change system should be contained in a perfectly conducting container.
  • Perfect isothermal change is impossible but when a change is carried out very slowly approximate isothermal change occurs.
  • It follows Boyle's law.
  • Work done in the isothermal process is graphically given by the area under the P-V curve.
  • ∆H = nCp∆T  and  ∆H = nCv∆T
              In isothermal process ∆T = 0
                                             => ∆H = 0 and ∆E = 0
  • Specific change at constant T is infinitely great in the isothermal process.

2. Adiabatic process:

        There is no heat exchange between the system and surroundings.
             q = constant
        => dq = 0
        Perfectly adiabatic change is impossible but when a process is carried out very rapidly fairly
        approximate adiabatic change occurs.

3. Isobaric process:

              It is the system in which pressure of the system remains constant during each step.
              P = constant , dp = 0

4. Polytropic process:

         In this process heat capacity of the body remains constant.
            Cp = constant  and  Cv = constant

       => dCp = 0  and  dC = 0

5. Quasistatic process:

         The process in which the deviation from thermodynamic equilibrium is infinitesimal and all the states through which the system passes can be considered as equilibrium states.

6. Isochoric process :

         When there is no change in the volume of the system during various operations the change is said to be isochoric.
       V = constant  => dv = 0
    For example, the combustion of a substance in a bomb calorimeter is an isochoric process.

7. Cyclic process:

           The process which brings back a system to its original state after a series of changes is called acyclic process.
   As the E and H depend only on their states, E and H are constant.
   So, dE = 0 and  dH = 0

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