by jasper » 17 October 2015, 16:20
Which physical properties you need depends on your purpose. Are these compounds always appearing in solution, and never as a solid? Then by good approximation they will be always in the liquid phase, but next you would want to know whether the vapor-liquid equilibrium is affected by the presence of these compounds. If this is not relevant to you, use an activity model to describe the liquid phase perhaps and assign a really high vapor pressure to these compounds (could be a constant value) which will force these compounds to be largely in the liquid phase. All that remains is sufficient information for enthalpy: you will need to choose the combination of ideal has heat capacity and heat of vaporization (they are added up to predict the liquid enthalpy) such that any heat balance is predicted well. Of course if heat balances are not important to your application either, you can pick a rough estimate there (e.g. use whatever you can find on any bio compound).
In other words: you will have to define the requirements for your application prior to selecting which physical properties you need.