Is Heat Capacity Derivable for Non-Ideal Liquid Mixtures?

[Gvozden]

Can I derive heat capacity of one phase mixture of three liquids as a sum of their mass shares multiplied by heat capacities of solitary components at given temperature? All components are miscible, of course ... thank you in advance

 

[BvU]

Hello Gvozden, $\qquad$ $\qquad$ !

You certainly can -- no one will stop you

In doing so, you make the assumption that the interaction parameters between the three compounds can be ignored. As a mixing rule, that is often good enough...

 

[Gvozden]

BvU, i could multiply the sum with Planck's constant, and still no one would stop me, wouldn't it? But it would make the result false.

As a matter of fact, third liquid serves as a cosolvent for two, otherwise non miscible liquids, changing two phase system into a single phase. Cosolvent does not participate in any kind of reaction, but there is a reaction between the other two liquids, thus only agitated by several types of intensification (microwave, ultrasound, laser, cavitation, conventional heating...)

Due to your response and advise, am I right to think that it is not advisable to calculate heat capacity like I asked to, and to measure heat capacity of the mixture by calorimetric bomb?

 

[BvU]

Ah, we are quickly exceeding my (nevertheless non-negligible) pay grade and have to call in some experts. @Chestermiller , for example.

Best advice I can give before starting bombing would be to consult a properties program like Aspen Properties (at least, if your components can be found there). Or dig around in the literature...

 

[Chestermiller]

You can use the ideal mixing rule only for an ideal mixture. This is not an ideal mixture, as evidenced by the immiscibility of two of the components. So you are stuck measuring the heat capacity of the mixture experimentally. It sounds like if there is a chemical reaction, there is also going to be a 4th component present?