To calculate this composition, account must be taken of the above equilibria between the three different carbonate forms (H2CO3, HCO3− and CO32−) as well as of the hydration equilibrium between dissolved CO2 and H2CO3 with constant formula_3 (see above) and of the following equilibrium between the dissolved CO2 and the gaseous CO2 above the solution::CO2(gas) CO2(dissolved) with formula_4 where kH=29.76 atm/(mol/L) at 25 °C (Henry constant)The corresponding equilibrium equations together with the <math>\scriptstylerelation and the charge neutrality condition <math>\scriptstyle[H^+=result in six equations for the six unknowns [CO2, [H+, [HCO3− and showing that the composition of the solution is fully determined by formula_2.