what is Physical significance of Enthalpy for a process where we don't have pressure constant
The enthalpy is a state function defined in terms of the internal energy and PV. It has no special physical significance, but is very convenient to work with in many kinds of problems. It is particularly convenient for quantifying the effect of temperature on the conditions for phase equilibrium and chemical equilibrium. It is also very convenient to work with in doing energy balances on industrial processing systems operating at steady state, such as chemical reactors, heat exchangers, distillation towers, compressors, absorbers, etc. Please just be patient and, as time progresses, you will get a good appreciation for its utility.
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