So in my coursebook it says enthalpy is a property that accounts for the increase in internal energy and the accompanying work done by the system and that its equal to the sum of the internal energy $U$ and product of pressure $P$ and volume $V$. Also on the net, mostly on the internet it says:

A thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume.

And where it explains in other words I don't quite understand, e.g. as on Wikipedia. So please I would like anyone of you to explain (in beginner terms) that what is the meaning of enthalpy and heat content as used in the definition above.


2 Answers 2


In my judgment, it's not worth spending much of your valuable time trying to assign physical significance to the physical property we call Enthalpy. Enthalpy is just a convenient parameter to work with when we are doing certain types of thermodynamic analysis. One situation which it is particularly useful for is in applying the first law to open systems in which material is entering and/or leaving the system. Another is where changes in a closed system are occurring at constant pressure.


I got this from Wikipedia:

The $U$ term can be interpreted as the energy required to create the system, and the $pV$ term as the energy that would be required to "make room" for the system if the pressure of the environment remained constant. When a system, for example, $n$ moles of a gas of volume $V$ at pressure $p$ and temperature $T$, is created or brought to its present state from absolute zero, energy must be supplied equal to its internal energy $U$ plus $pV$, where $pV$ is the work done in pushing against the ambient (atmospheric) pressure.

I think it answers my question. Enthalpy is just a property of system we defined essentially to make it easy to calculate the heat of the reaction as Chester Miller says, but its definition is the energy present as particular kinetic and potential energies in addition to the energy needed for the system to exist in its present condition by doing work against the surroundings.


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