Isochoric Process (Constant Volume Process)

An Isochoric process, also called a constant volume process, an Iso-volumetric process or an isometric process, is a thermodynamic process during which the volume of the closed system undergoing such a process remains constant. The Isochoric process here should be a quasi-static process.

  • P,V,T Relationship:
                                    P/T = Constant
  • Work done by the gas:
                                    W1-2 = P (V2-V1) = 0
  • Change in Internal Energy:
                                    dU  = mCv (T2-T1)
                                    U2 - U1 =
mCv (T2-T1)
  • Heat Supplied or heat transfer:
                                    Q1-2 = dU + W1-2
                                    Q1-2 =
U2 - U1 = mCp (T2-T1)
  • Change in Enthalphy:
                                    H  = mCp (T2-T1)

Important Note:
  • The change in internal energy (dU) and the change in enthalphy (dH) have the same expression for each process.
  • During expansion or heating process, work is done by the gas (i.e. W1-2 is +ve); internal energy of the gas decreases (i.e. dU is -ve) and the heat supplied to the gas (i.e. Q1-2 is +ve).
  • During compression or cooling process, work is done on the gas (i.e. W1-2 is -ve); internal energy of the gas increases (i.e. dU is +ve) and the heat supplied by the gas (i.e. Q1-2 is -ve).

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