Henry-Law Constants: State the Concentration-to-Pressure Convention

Define the Interface or Transport Basis

IUPAC distinguishes the concentration-over-pressure solubility constant from the pressure-over-concentration volatility constant. Both definitions refer to equilibrium at infinite dilution. For the matched p-and-c convention, their units are reciprocal, so multiplying by pressure is appropriate for one and dividing by it for the other.

Review a Hypothetical Comparison

In an invented dilute equilibrium example at a fixed temperature, dissolved concentration c=0.24 mol/m³ corresponds to partial pressure p=2000 Pa. The concentration-over-pressure ratio is 0.00012 mol/(m³·Pa); its reciprocal is approximately 8333.33 Pa·m³/mol. Multiplying 0.00012 by 2000 or dividing 2000 by 8333.33 gives the same 0.24 mol/m³. Treating 8333.33 as a concentration-over-pressure number would instead change the dimensions and produce a meaningless result.

Keep the Evidence with the Decision

Write c=Hs·p or p=Hv·c above the calculation. Identify the gas species, solvent, temperature and concentration convention, including whether p is that species' partial pressure. Convert units before comparing constants. Confirm that the dilute-equilibrium definition applies rather than using a tabulated value to describe a rapid nonequilibrium uptake trace.

The example numbers are synthetic and describe no named gas. They are not a solubility recommendation for a formulation or an extrapolation across temperature.

Are the constant units and equation direction compatible with the gas-solubility calculation?

This blank worksheet is for your own project. It contains no H M machine trial result.

Customer Questions

Primary References

These references support the technical principles discussed in this guide. The worked examples and review questions are educational.

• the concentration-over-pressure solubility constant
• the pressure-over-concentration volatility constant
• Reference from hmpharmamachines.com