# How are thermodynamics properties of gases and liquids calculated numerically?

I was wondering how the values of thermodynamic properties as enthalpy, entropy, internal energy, specific heat, specific volumes ... etc, of gases and liquids are calculated using programming libraries such as cantera and thermopy as an example.

How are steam tables made for instance? How do we get all these values of properties if not experimentally?

• Interesting question. If no one here has the expertise to answer, you might find the right person on physics.SE. If that is a route you want to take, then you can flag your question and ask a moderator to migrate it for you. Jun 11 '15 at 21:39
• Chris, nice suggestion, but I will die before I let this question be migrated. It's too perfect for our site. Jun 12 '15 at 3:22
• Would you have a specific problem with experimentally generated data? Jun 12 '15 at 22:00
• @rul30 Actually no one has. But say if you were engineering a water boiler would you consider a measurement set-up for every property you need in your design?
– Algo
Jun 13 '15 at 2:19

If you assume the gas you are dealing with is a semi-perfect gas (e.g. the heat capacity is not a function of pressure, and the gas follows ideal gas law), then you can calculate all properties (in the order of enthalpy, internal energy, entropy and gibbs free energy) if you can measure the specific heat capacity at constant pressure (cp, sometimes, a fitted polynomial) base on the basic relations. E.g. $dh=cpdT$, $u=h-RT$, $ds=(dh-vdp)/T$, etc