Isobaric Process

An isobaric process is a thermodynamic process in which the pressure stays constant. The term derives from the Greek iso-, (equal), and baros (weight). The heat transferred to the system does work but also changes the internal energy of the system:

According to the first law of thermodynamics, where W is work done by the system, U is internal energy, and Q is heat. Pressure-volume work by the closed system is defined as:

where Δ means change over the whole process, whereas d denotes a differential. Since pressure is constant, this means that

.

Applying the ideal gas law, this becomes

assuming that the quantity of gas stays constant, e.g., there is no phase transition during a chemical reaction. According to the equipartition theorem, the change in internal energy is related to the temperature of the system by

,

where is specific heat at a constant volume.

Substituting the last two equations into the first equation produces:

,

where is specific heat at a constant pressure.

Read more about Isobaric Process:  Specific Heat Capacity, Sign Convention For Work, Defining Enthalpy, Variable Density Viewpoint

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