Thermo Calculation for Diluting 2.5% H3PO4 at 353°C to 100°C with Water

[sout528]

Hi there

If I have 2.5% H3PO4 at 353 degrees C and I need to bring the solution down to 100 degrees C only by adding any amount water, how do I go about the thermo calculation? I need final temperature and amount of water (thus final concentration... likely <0.1 M? ) Heat capacity approaches 1 as concentration approaches 0, and the heat of dilution approaches 0 in the same way. Thanks for any advice.

 

[Borek]

That's just a heat balance, but as you start close to critical point the main problem is that the heat capacity changes. Instead of using q=mcΔT you need to use

$$q = m\int c dT$$

and integrate from T_start to T_final.