I am not trying to disprove the chemistry. The chemistry is good on paper. The problem with seeing it as an open or closed system is in an open system there are many asumptions we have to make. In closed system we know what the exact chemistry is due to the fact we put it in there. The pressure issue is gasses are seen at different concretions at different pressures. Take a soda pop for example here. Pop the top and the CO2 in the liquid just dropped. You are looking at other problems with these indexes due to many variables that you to assume when you have liquid to atmosphere interface. We cant really predict the out gassing gases across this interface as a constant due to atmospheric conditions. We can get close but not close enough to be a constant.
Well past my bed time. Have a good day and don't work to hard, zzzzz
Steve