Thanks Brian,
Sorry for the delay in getting back to you. What you say makes intuitive sense.
Because my temperature range of interest is 10C - 150C, the extrapolate option is not entirely wise at this stage, for the reasons you highlighted.
What I did do is try to get to the bottom of what causes the unphysical jump based on your response, by suppressing MgH2SiO4, but that didn't do it. I then additionally, and in succession, suppressed NaH3SiO4, CaH2SiO4, Mg(H3SiO4)2, Ca(H3SiO4)2, H4(H2SiO4)4----, H6(H2SiO4)4--, CaH3SiO4+, MgH3SiO4+, but I still get the H2 concentration jump going from 25C to 26C, which baffles me..
Any additional insights?
Thanks for your time.
wr1.txt