Isobaric Process (Constant Pressure Process)

An Isobaric process is a thermodynamic process in which the pressure stays constant: ΔP = 0. 

• P,V,T Relationship:

                                    V/T = Constant

• Work done by the gas:

                                    W_1-2 = P (V₂-V₁)

• Change in Internal Energy:

                                    U₂-U₁ = mC_v (T₂-T₁)

• Heat Supplied or heat transferred:

                                    Q_1-2 = mC_P (T₂-T₁)

• Change in Enthalpy:

                                    H₂-H₁ = mC_P (T₂-T₁)

 

Important Note:

• When the gas is cooled at constant pressure, there will be a compression. The temperature and volume will decrease during cooling and work is said to be done on the gas.
• During expansion or heating process, work is done by the gas (i.e W_1-2 is + ve); internal energy of the gas increases (i.e dU is + ve) and heat is supplied to the gas (i.e Q_1-2 is + ve).
• During compression or cooling process, work is done on the gas (i.e W_1-2 is - ve); internal energy of the gas decreases (i.e dU is - ve) and heat is rejected by the gas (i.e Q_1-2 is - ve).