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a program to calculate gas volumes, fugacities and activities in the C-H-O system


CHO is a program which allows the user to derive molar volumes, fugacities and activities for H2O, CO2, CH4, H2 and CO and perform speciation calculations at fixed P, T and fO2 in the O-H and C-O-H systems. It uses the CORK equation of state (Holland & Powell 1991, CMP 109, 265-273) for all COH gases and additionally allows use of the Pitzer & Sterner equations (Pitzer & Sterner 1995, Int J Thermophys 16, 511-518) for H2O and CO2. For gas mixtures the program uses the Van Laar mixing model as outlined in Holland & Powell (2003, CMP 145, 492-501) but also allows this to be overridden in favour of ideal mixing.

The program opens with a main panel which allows the user 3 options:

1) Calculate molar volume or fugacity of individual gas species over a range in P and T

2) Calculate speciation in a gas mixture as a function of T at fixed fO2 and P or as a function of fO2 at fixed P and T. If the user specifies graphite/diamond presence the results will be in the COH system otherwise results will be calculated in the OH system. The program uses diamond or graphite depending on the PT conditions requested.

3) Calculate activity-composition relations for a pair of gases in a binary mixture of choice at fixed P and T


The executables, sample input files, and an info file explaining the use of the program are available here (OSX version is now 64bit):

download: mac OSX version

download: Windows version

download: Linux version

** updated for bug Jan 2019. Input for mixed gases incremented logfo2 relative to known buffers wrongly **