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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