Engineering
Dalton partial pressure and Henry equilibrium concentration formulas
Calculate ideal-mixture partial pressure and dilute-solution equilibrium concentration with an explicitly defined Henry solubility coefficient.
Keep pressure units and the Henry coefficient convention consistent
For an ideal gas mixture, component partial pressure is its mole fraction times total absolute pressure: p=y*P. Here P and p are in atmospheres and y is between zero and one. A volume fraction equals a mole fraction only under the appropriate ideal-gas assumptions; gauge pressure must first be converted to absolute pressure.
This example defines the Henry solubility coefficient as concentration divided by partial pressure, in mol/(L·atm), at a fixed temperature and solvent composition. Other references use the reciprocal coefficient or different units; copying their numeric constant directly would give the wrong result. Henry behavior is a dilute-solution equilibrium approximation, not a prediction of the rate of dissolution.
The supplied coefficient 0.0013 is an illustrative input, not a universal oxygen constant. Use a measured coefficient for the actual temperature, solvent and gas. Nonideal gas behavior, chemical reactions and changes in temperature can require a different model.
| Quantity | At P=3 atm, y=0.32 | At P=5 atm, y=0.32 |
|---|---|---|
| Partial pressure | 0.96 atm | 1.60 atm |
| Equilibrium concentration using the supplied coefficient | 39.94 mg/L | 66.56 mg/L |
Dalton's Law Component Partial Pressure P_i = y_i * P_total
Multiplies gas mole/volume fraction B3 by total absolute pressure B2.
=IF(COUNT(B2:B3)<>2,"Invalid inputs",IF(OR(B2<0,B3<0,B3>1),"Invalid inputs",ROUND(B3*B2,4)))Henry's Law Dissolved Gas Concentration in mg/L = k_H * P_i * MolarMass * 1000
Multiply mol/L by molar mass in g/mol and then by 1000 mg/g. The result is mg/L; it is not generally identical to mass-based ppm without accounting for solution density. This worksheet is a gas-equilibrium example, not a diving exposure or safety calculator.
=IF(COUNT(B2:B5)<>4,"Invalid inputs",IF(OR(B2<0,B3<0,B3>1,B4<=0,B5<=0),"Invalid inputs",ROUND(B4*B3*B2*B5*1000,2)))Try the example
Use the original values or change them to test your understanding.